Abstract:
A microprocessor controlled, general purpose gene synthesizer for programmably synthesizing selected nucleotide sequences. Depending upon a programmed chemistry, metered volumes of selected bases and reagent/solvents are sequentially metered into the bottom of a reaction cell containing solid-supported nucleotides, where desired linkages are achieved in an agitated suspension. Self-refilling syringe metering and electrically initiated, pneumatically operated valving insures economical, non-contaminated synthesis. Preprogrammed, selectable chemistries and operator programmed sequences are operatively coupled under microprocessor control to ensure a general purpose synthesizer.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to gene synthesizers and in particular to a general purpose, programmable oligonucleotide sequence synthesizer, operable in response to a pre-programmed linking chemistry and an operator selected nucleotide sequence. 
     Along with the evolution of an understanding of the function, structure and chemical makeup of nucleotide sequences, such as DNA, so too has an awareness evolved as to the practicalities and feasibilities of genetic engineering. Such engineering efforts, however, require a complete understanding of the chemical and biological reactions in cells. While recent efforts have demonstrated that desired bacterial mutations having desired properties can be engineered, such efforts have been very costly in terms of time, money and equipment. 
     The most practical of such cellular or genetic engineering efforts, to date, have been achieved via a building block approach that starts with the identification of a desired sequence of nucleotides and progresses to the growth of the desired nucleotide suquences from the component bases; to the modification of identified DNA molecules with the grown sequences; and finally to the seeding of host bacteria with the modified DNA so as to cause the production of the modified DNA via the reproduction of the cells having the sought-after modified DNA characteristics. The success of such processes thus require the linking of a desired nucleotide sequences with appropriately fragmented DNA sequences at desired sites so as to modify the DNA. The modified DNA is then introduced and reproduced by host cells, that are chemically tricked into accepting and reproducing the modified DNA. Such reproduction may also be enhanced via various so called &#34;promotors&#34; which are added to the modified gene. Sufficient quantities of the thus modified genes or protein are then grown via apparatus that promotes the growth of the seeded hosts and at the same time the modified DNA so as to replicate vast numbers of the seeded host bacteria and thereby the modified DNA. 
     Basic to such genetic engineering efforts is the synthesis of desired nucleotide chains from an initial mononucleotide. In this regard, electro-mechanical apparatus has been developed for synthesizing desired oligonucleotide sequences via the sequential linking of desired bases to a starting or &#34;seed nucleotide.&#34; For example, various synthesizing apparatus has been developed by a number of companies, such as the Model 280 synthesizer by Vega Biochemicals, the Model 380A by Applied Biosystems and the DNA/RNA synthesizer developed by the Biologicals Company. The details of such apparatus can be obtained upon reference to the sales literature and various other published literature from these companies as well as upon reference to an article in High Technology, Volume I, No. 1 pp. 60-68 (September/October 1981). 
     While the above synthesizers offer alternative methods for synthesizing desired nucleotide suquences, each suffers from various shortcomings, such as excessive reagent waste or programming limitations as to the type of chemistry that can be employed. Furthermore, such synthesizers are relatively difficult to operate, maintain and refill with the necessary base/reagent/solvent materials. 
     The present invention, however, overcomes the above problems and incorporates the above desired features in a general purpose, programmable, micro-processor controlled synthesizer. In particular, the present apparatus is expandable to perform any of the three basic, generally accepted chemistries (i.e. phosphoramidite, phosphate triester or phosphite triester), although the embodiment disclosed hereinafter is of the phosphate type. (A more detailed description of such chemistries can also be found among other places in Nucleic Acids Research Volume 10, No. 5, pp. 1755-1769 (1982) and Hendrickson et al., Organic Chemistry, Chptr. 25-5, pp. 1007-1011 (1970)). Thus, depending upon the selected chemistry and its associated sequence of subroutines, the present apparatus successively meters programmed volumes of the process dependent base/reagent/solvents into a reation cell, and there the desired nucleotide sequences are grown in a liquid suspension on a solidsupport material. While the chemical process may be varied, the present apparatus generally operates to sequentially wash and dry the contents of the cell, expose desired nucleotide reaction sites, add and couple desired bases at the reaction sites and cap or protect the reaction sites, until the next base addition. This process then continues until a desired growth sequence is complete and after which the grown oligonulceotide is chemically separated from the solid support material. 
     The above objects, advantages and distinctions of the present invention as well as various others will, however, become more apparent upon a reading of the following description and upon reference to the following drawings. It is to be recognized though that while the following description is made with respect to the presently preferred embodiment, various changes (and some of which will be mentioned hereinafter) may be made thereto without departing from the spirit and scope of the present invention. 
     SUMMARY OF THE INVENTION 
     A general purpose, programmable oligonucleotide synthesizer. The apparatus essentially comprises a plurality of base/reagent/solvent reservoirs; valve means for steering desired volumes of the base/reagent/solvents per a desired sequence and to selected hydraulic paths; syringe means for metering selected ones of the base/reagent/solvents; a bottom-fed reaction cell containing liquid suspended solid-support materials having seed nucleotides bonded thereto; and a preprogrammed controller means operative in response to a selected chemistry and programmed nucleotide sequence. Additionally, means are provided for agitating the liquid suspended solid-support materials in the reaction cell during the growth process, as well as means for heating the reaction cell so as to promote the growth process. 
     The controller essentially comprises a programmable read only memory (ROM) and a random access memory (RAM) based program store for containing the pre-programmed chemistries; a RAM memory for containing the operator programmed oligonucleotide sequences; a RAM based processing unit for controlling internal/external communications, sequencing and timing; driver means for actuating selected flow paths; and vibrating and heating means for appropriately promoting chemical reactions. The apparatus also provides for the selective metering of the relatively less espensive base/reagent/solvent materials from relatively large supply reservoirs via pneumatically actuated, chemically inert, pressurized solvent handling valves and conduits and the more expensive materials via a self-filling directional syringe assembly. The syringe assembly, comprises a plurality of syringes coupled to directional valves so as to either permit the metering of a desired volume of base/reagent material into the reaction cell or into the reservoirs supplying the syringe assembly, while ensuring that each of the syringes is refilled during each cycle of each linking sequence. The reaction cell, in turn, comprises a chamber adaptively formed for receiving variously sized and shaped inserts so as to control the internal liquid volume of the cell. 
     In operation, the base/reagent/solvent materials enter the bottom of the cell and support in suspension appropriate solid-support materials having seed nucleotides attached thereto for appropriate amounts of time. During the coupling time, the associated vibration and heater means, and which too are responsively coupled to the controller, promote the linking of the selected base or bases to the seed nucleotide. Associated waste and test means ultimately collect the waste base/reagent/solvent materials and/or test the waste to determine whether or not appropriate linking actions have occurred. Additionally, the reaction cell is mounted so as to permit an operator to visibly monitor the cell effluent for color and flow during the various control sequences (most typically during detrytilation). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a system block diagram of the present general purpose oligonucleotide synthesizer. 
     FIG. 2 shows a perspective view of the primary mechanical elements contained in the present apparatus. 
     FIG. 3 shows a detailed cross sectional view of the reaction cell. 
     FIG. 4a shows a detailed exploded view of the vial reservoirs. 
     FIG. 4b shows a perspective view of a typical septum port injection which may be added for di-mer or tri-mer containing processes. 
     FIG. 5 shows a detailed view of the syringe body. 
     FIG. 6 shows the hydraulic flow paths for the base/reagent/solvent materials as they traverse the various valves and syringes. 
     FIG. 7 shows a generalized schematic diagram of the control and communications circuitry. 
     FIG. 8, comprised of FIGS. 8a and 8b, shows a detailed schematic of the process controller. 
     FIG. 9 shows a flow chart of a typical base delivery and reaction sequence. 
     FIG. 10 shows a flow chart of a typical DMF wash sequence. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a generalized system block diagram is shown of the present synthesizer and which is essentially comprised of a number of base/reagent/solvent reservoirs 10, process controller 12, a bottom-fed reaction cell 14 and associated valve bodies 16 and syringe assembly 18. During normal sequencing, the controller 12 in response to a plurality of pre-programmed subroutines, an operator programmable nucleotide coupling sequence and various process parameters, successively causes the adding of desired bases and reagents to the reaction cell 14 and performs various intermediate solvent washes so as to ensure the uncontaminated growth of the desired oligonucleotide sequence. A vibrator 20 and heater 22 are also included and under the contol of controller 12 promote the linking action. In turn, as the various bases are added to the cell 14 and linked to the seed nucleotides contained therein on a solid-support material the various sequences and valve operations and flow directions are displayed on a display 24. The waste is collected via the waste collector 26 or depending upon the system, test apparatus 28 may earlier sample the waste to determine that the desired reactions have taken place. Alternatively, the reaction cell 14 and portions of the associated low transfer volume clear connecting tubing are visible to the operator on the front panel so as to permit the inspection of the colored reactions and determine whether or not desired reactions have occurred and as evidenced by the coloration of the solution exiting the reaction cell 14. Presently, such visibe monitoring is most often performed during detrytilation; however, due to the length of most sequences, the earlier mentioned use of test equipment is preferred and is achieved via among other appartus, an automatic sampler and associated spectrophotometric test equipment. 
     While the chemistries employed to promote the linking of desired bases are generally known, although rather complex, the present apparatus simplifies the process by automatically ensuring that the proper base/reagent/solvents are introduced into the reaction cell 14 at the appropriate times and for the proper amounts of time during the growth cycle so as to ensure both the completeness of the reaction and that the proper nucleotide sequence is grown. In fact the present apparatus has been formed to provide a 100% yield in some processes of up to 20 or more linkings. As the proper base/reagent/solvents are introduced into the cell 14, the controller 12 also operates for appropriate amounts of time to cause the vibrator 20 to vibrate or mechanically mix or agitate the granular solid-support material containing the &#34;seed&#34; nucleotides with the introduced base/reagent/solvents so as to make the introduced chemicals available to all the seed nucleotides for optimum chemical reactivity. The heater 22, in turn, is controllably operated for appropriate amounts of time so as to promote the chemical bonding during mixing. It is to be noted though that depending on the chemistry and volatility of chemicals or reaction times, the duration and sequence of heating/mixing may be varied and/or deleted. It is also to be noted the seed nucleotides within cell 14 are generally all of one type so that a number of the desired, identical oligonucleotide sequences are grown at the same time. 
     The valve means 16 and syringe means 18, like the vibrator 20 and heater 22, are controllably actuated by the controller 12 so as to introduce the appropriate base/reagent/solvents in accordance with the synthesis program and subroutine sequences of Tables 3 and 4 and which will be discussed hereinafter. Depending upon which base/reagent/solvents are selected for a specific sequence, the controller 12 causes the selected base/reagent/solvents to be delivered via associated ones of the valve means 16 and/or the syringes 18 and their associated low dead volume flow paths to the bottom of the reaction cell 14 so to as float in suspension the solid-support material containing the seed nucleotides. At this point, it should be noted that the valves 16 and syringes 18 and their associated flow paths are organized into groups that depend upon the reactivity of the chemicals and which groups are further isolated from one another so as to prevent against unwanted contamination (either in a liquid or vapor form), but which too will be discussed in detail hereinafter. Also, depending upon the cost of the chemicals and the frequency and the volume thereof that is used during normal sequencing, the base/reagent/solvents are either delivered directly from the syringe assembly 18 or from various of the larger pressurized containers 10. 
     The chemical linkings in the reaction cell 14 thus occur in an agitated suspension. Upon the expiration of each linking period during a series of neutralization and washing steps, the waste chemicals are, in turn, typically flushed from the cell 14 via the introduction of appropriate amounts of solvents and non-reactive materials into the bottom of the cell 14. During the nitrogen (or argon) &#34;blow down&#34; step, however, and which dries the support material with its attached DNA chain following the washing steps, the gas is introduced into the top of the cell 14 and the waste chemicals present in the cell 14 are flushed out the bottom. In all cases the waste chemicals are then delivered to the waste collector 26, except for the detritylation step and for which the chemicals are delivered to an external collector 28 and tested via known techniques and spectrophotometric test and recording apparatus to determine that the desired chemical reaction has taken place. 
     Simply put, therefore, the present apparatus during each cycle or linking sequence, selectively introduces desired base/reagent/solvents to the reaction cell 14 so as to create a fluidized bed that, in turn, is heated and/or vibrated to promote chemical bonding. Depending upon the chemistry, each cycle or bonding step for each base or mixed-base (including di-mers or tri-mers) proceeds in a similar fashion as dictated by the chemistry, until the desired nucleotide sequence has been grown. 
     Referring now to FIG. 2, a partially sectioned perspective view is shown of the present apparatus with various portions of the cabinet 28 and its front cover 30 removed. From this view, the primary elements of the present synthesizer can be seen in their relative positionings with respect to one another and the metal cabinet 28. In particular and looking to the normally exposed portion of the front panel 31, only the back-lighted hydraulic flow map 32 and temperature controller 34 are visible to the operator. While the flow map 32 will be discussed in greater detail hereinafter as it relates to the front panel, it generally comprises a back lighted display 32 whereon the various pressurized syringes, reservoirs and valve bodies are shown so as to provide the operator with a visible indication of what reservoirs and flow paths are selected and are operational at any point in time. Thus, the operator can, at a glance, determine what portion of the synthesis cycle is active. 
     The temperature controller 34, in turn, provides the operator with pertinent temperature information as it relates to the reaction cell 14 and whether or not heat is being applied. The temperature controller 34 will, however, not be described in any detail, since it too is the subject of a presently co-pending patent application (i.e. Serial No. 06/377,627), assigned to the present Assignee. Suffice it to say that the temperature controller 34 generally monitors the temperature of the reaction cell 14 and which is heated by an epoxy encapsulated thin film heater/sensor element 36 that is wrapped about the reaction cell 14. The temperature of the reaction cell 14 is set and read via a set/read switch 38, while the power to the controller 34 (including all over circuitry) is applied via an on/off switch 40. The temperature, in turn, is displayed on a liquid crystal display 42 and which also displays the &#34;set&#34; temperature as it is adjusted via the adjustment knob 44. Power, on the other hand, is applied to the thin film heater/sensor 36 and reaction cell 14 via plug jack 46 and multiwire conductor 48 so as to ensure that the fluidized bed within the reaction cell 14 is subjected to desired temperatures during the appropriate phases of each cycle. 
     Referring now to the various apparatus attached to the internal recessed portion of the front panel 31, this portion of the panel 31 generally contains a plurality of syringe bodies or assemblies and associated supply reservoirs in the form of reagent vials 50, along with the reaction cell 14 and syringe speed of movement adjusting screws 52. These latter adjusting screws 52 are used to regulate the air flow from the pneumatic cylinders that are used to control the movement of the syringe plungers 97. The overall system air presure, in turn, is provided in a range on the order of 45 to 60 psi. and is used to operate the various pneumatically actuated mixing/delivery valves and air actuator that too will be described in detail hereinafter. 
     Turning attention to the reaction cell 14, it is removably mounted to the front panel 31 via a specially designed clamp or holder 58 which, in turn, is coupled to a vibrating means (not shown) that is mounted behind the panel 31. Thus, the clamp 58 and cell 14 vibrate upon actuation of the vibrator means. This mode of agitation is felt to be preferable to that offered by other manufacturers in that it minimizes the complexity of the apparatus and in conjunction with the fluidized bed ensures the exposure of all the base seeded resin particles to the dissovled solvents/bases/reagents. It is also to be noted that the vibrator is attached to the cabinet 27 via well known dampening bumpers so as to minimize any undesired vibration that might otherwise be induced in the panel 31 or cabinet 27. 
     Attached to the top and bottom of the cell 14 are, in turn, a pair of threaded couplers 60 which couple the supply and waste tubing 62a and 62b to the cell 14 in a compression fit fashion. While other known means of attachment are acceptable, it should be noted that the tubing 62 as well as all other chemical containing tubing of the present apparatus should be of a low dead volumn type such as for example a teflon tubing having a 0.020 inch I.D. Such tubing has been found to be capable of withstanding operating pressures and minimizes the wasting of the chemicals. 
     Attention is now also directed to FIG. 3 wherein a detailed cross-sectional view is shown of the reaction cell 14 along with its various components. Generally, the reaction cell 14 is fabricated from an appropriate non-reactive, heat transferring material, such as type 316 stainless steel, and is formed to permit the disassembly and changing of the liquid volume size of the cell 14. In particular, the cell 14 is comprised of a body member 64 that is threaded to receive the upper and lower fittings 60 and tubing 62. Between the fittings 60, the cell 14 contains removable inserts 65 and 66, each of which have grooves formed therein for receiving &#34;O&#34; rings 67 at the interfaces between the couplers 60 and the inserts 65 and 66 and frits or filters 63 at the top and bottom. The inserts 65 and 66, are presently formed so as to create a frustoconical chamber 71, but it is to be recognized that various other chamber shapes and sizes are easily achieved by varying the manufacture of inserts 65 and 66. The chambers 71 as presently available are also sized to contain liquid volumes on the order of 100 microliters to 500 microliters. The cell inserts 65 and 66 are also conveniently formed so as to allow the direct weighing of the seeded resin in the cell 14 prior to beginning a synthesis sequence, thus minimizing handling. 
     At this point, it should also be recognized that while the present description is made with respect to a single reaction cell 14, conceivably a number of such cells could be coupled to the present apparatus. Each such additional cells 14 could then, too, either be vibrated and/or heated as desired and within which identical or different sequences could be grown, depending on the programming of the controller 12. Such additional cells 14 then, too, could be operated in parallel or sequentially so as to optimize the through-put of the present apparatus. 
     Returning to the description of FIG. 2 and with continued attention to FIG. 1, mounted immediately above the reaction cell 14 are a number of reagent vials 50 and which are used as supply reservoirs for the syringes 72 of the syringe assembly 18. The reagent vials 50 are mounted to the front of the panel 31 in a removable fashion via a plurality of holders 64 and which facilitate the removal and refilling of the vials 50, at or near depletion. The vials 50, in turn, each contain a cap having a septum sealed syringe port and pressurized lines 68 coupled thereto so as to facilitate the flow of the base/reagents into and out of the vials 50 via color coded fluid lines 70. It is to be noted that dry nitrogen or argon is used as the pneumatic medium for pressurizing the reservoirs 10, including the vials 50, and which is chemically inert to the various chemicals used with the present equipment. 
     Directing attention to FIG. 4a, a detailed and disassembled view is shown of the present syringe supply vials 50. Specifically, each of the vials 50 is comprised of an elongated, test tube-like, glass vial body 74 into which a threadably secured syringe port 76 is secured via a lock nut 78. A septum cap 80 and septum 82 are, in turn, threadably secured into the top of the syringe port 76 and which permit the refilling of each vial body 74 without discontinuing operation of the present equipment. Completing the structure of each vial 50 are associated compression fittings 84 for compressably securing the pressure lines 68 and fluid lines 70 to the syringe port 76. It is to be noted, too, that while the pressure lines 68 terminate at the syringe port 76, the supply lines 70 extend into the glass vial body 74 so as to submerge the inlet to the fluid lines 70, thus ensuring proper liquid pick-up. 
     FIG. 4b on the other hand shows a perspective view of a septum port injector 69 such as manufactured by Scientific Systems, Inc., and which although not shown in FIG. 2 may be added as desired. Such an injector 69 is comprised of a body 73 containing a septum (not shown) that is accessible to a syringe inserted through the threaded closure stem 75. In operation, one or more of such injectors 69 may be added to the panel 31 in series in the supply line 62a to the reaction cell 14 or be isolated from one another so as to permit the injection of separately prepared di-mers or tri-mers of the bases into the reaction cell 14. Thus, the possible linking sequences can be further expanded, as well as the possible length of any given sequence and which could thereby be extended to 80 bases, if di-mers are used (such being the case since depurination has typically been encountered at 40 or more linkings). 
     Also, assuming the use of the septum port injectors 69, it then becomes possible to couple automatic injectors thereto, such as are used in high performance liquid chromotography (HPLC). Such injectors would further automate the present apparatus and permit fully automatic control as where the chemicals are arranged in a desired order relative to the injectors and which would appropriately be activated by the controller 12 relative to the programmed chemistry. 
     Returning again to FIG. 2 and mounted to the left of the vials 50 is the syringe assembly 18, and which is comprised of five or more syringes 72 that are mounted in a pneumatically driven rack 86 and which rack, in turn, is comprised of a valve body containing base member 88, syringe body holding member 90 and a plunger driving member 92. The driving member 92 is retractably mounted to right and left pneumatic cylinders 94, while the holding and driving members 88 and 90 are stationary. Each of the pneumatic cylinders 94 also have associated supply and return air pressure lines 98 and which are, as mentioned, interactively controlled via the speed adjusting screws 52 so as to permit the calibration and regulation of the exhaust air flow from the cylinders 94. Also associated with each of the push-rods 95 of the cylinders 94 are length adjusting means (not shown) and which in conjunction with the lower stationary &#34;L&#34; brackets 96 permit the adjustment of the length of throw of the cylinders 94. Thus, as air pressure is applied in either direction to the cylinders 94, the cylinders 94 raise or lower and thereby depress or retract the plungers 97 so as to deliver or recharge each of the syringes 72 with a known volume of chemicals. 
     For a more detailed view of the syringe assembly 18, attention is also directed to FIG. 5. From FIG. 5, the compression mounted cylinder travel adjusting nuts 99 are shown in detail relative to the push-rods 95 and the stationary L brackets 96 and their associated mounting hardware, (i.e. screws, rivets, etc.). Upon reference also to the syringes 72 and the various support members including holding members 88, 90 and plunger driving member 92, it is to be noted that the plungers 97 of each of the syringes 72 are mounted to the driving member 92 via separate clips 100 and knurled thumb screws 102 that are threadably secured to the driver member 92. Each of the heads of the plungers 97 are rigidly contained beneath one of the clips 100 via an associated thumb screw 102. Thus, as the plunger driving member 92 (and which is attached at its right and left ends to the cylinders 94) moves with the cylinders 94 so, too, do the syringe plungers 97 move in and out of the syringe bodies 72. 
     The syringe bodies 72, in turn, are mounted to the panel 31 via the two-part or split holding member 90, and which can be disassembled so as to permit the insertion and removal of the individual syringe bodies 72. It is to be noted, too, that each of the syringe bodies 72 are frictionally mounted within holes bored between the two halves of the holding member 90 via appropriate resilient interface material, such as split rubber or plastic bushings. The tips or nozzles of the syringe bodies 72 are, in turn, each coupled in a threaded fashion to an individual pneumatically actuated valve body 104 that is mounted to the back of the holding member 88. 
     Referring next to the valve bodies 104, in the preferred embodiment they are each typically comprised of a pneumatically actuated three-way valve and are each operable via an electrically driven solenoid that supplies air pressure to the actuator of the valve body 104. The valves 104 may, also each be operated manually to confirm operability via switch handles (not shown) that are mounted to the backs thereof. At normal operating pressures, though, the valves 104 do not permit manual actuation. In particular and during normal operation, the controller 12 acts through a plurality of associated electro-pneumatic solenoids (not shown) to pneumatically actuate and select only desired ones of the valve bodies 104, such that only the base/reagent contained within a selected syringe 72 is supplied via the selected valve body 104 to the reaction cell 14. At the same time, however, the others of the non-selected valve bodies 104 and syringes 72 are also actuated so as to return an equal amount of base/reagent via their associated supply lines 70 to their associated reservoir vial 50. After each syringe delivery of chemical, the controller 12 then selects all the valve bodies 104 and retracts the plunger drive member 92 so as to refill each of the syringes 72. Thus, measured volumes of base/reagent are economically supplied to the reaction cell 14 as needed during each growth cycle without wasting any of the rather costly chemicals. 
     It is also to be noted that at present the operator must periodically monitor the base/reagent/solvent containing supply reservoirs 106 so as to confirm whether or not they are near depletion. If they are near depletion, they must be refilled and which in the case of the supply reservoirs 50 merely requires injecting more chemicals through the septum cap 80. Alternatively, an alarm condition may be implemented to warn the operator and which would sound when the controller 12 confirmed that its record of base/reagent delivered to date exceeds a predetermined limit. In the latter event, upon refilling the vials 50 and clearing the alarm, normal operation would resume and each syringe 72 would continue to be refilled from its associated vial 50 at the end of each cycle. 
     Before continuing, it should be noted, too, that in the event of a power failure, the present apparatus is programmed to repeat only the last step performed or during which the power failed. Thus, while extra chemicals might be consumed in the repeated step, the sequence in process is not wasted. Also, it should be noted that provision has been made for saving any operator programmed information in the event of a power failure for up to approximately four hours so as to prevent against having to reprogram. 
     Returning again to FIG. 2, it is to be noted that a number of relatively large containers or reservoirs 106 have been mounted in to the back of the present synthesizer. These, typically, each contain one liter or 500 milliliters of a number of relatively less expensive chemicals, such as the solvents, and which containers 106 too are each pressurized via individual dry nitrogen or argon pressure lines 68. As with the vials 50, associated color coded supply lines 70 are, in turn, coupled from the containers 106 to various other three-way valve bodies 104 (not shown) that are represented on the hydraulic flow map 32 and which are mounted behind the panel 31. The specific groupings of valve bodies 104 associated with the base/reagent/solvent containing supply reservoirs 50 and containers 106 and the fl ow therebetween will however be described in greater detail hereinafter. It should also be noted that the containers or reservoirs 106 are pneumatically mounted on a rack 108 via air cylinders 110 and 112 so as to be simultaneously raised or lowered upon actuation of the raise/lower toggle switch 114. Also, mounted on the top of rack 108 are a number of pressure gauges 116 and regulator knobs 118 for controlling the nitrogen pressure on the reservoirs via pressure lines 68. 
     While to date and as mentioned a number of delivery approaches have been suggested, it should be apparent from the above that the present delivery system, due to the simplicity of its mechanical configuration, requires a minimum number of operating control functions and circuitry. Also, due to the use of low transfer volume delivery lines 70 and syringes 72, the amount of chemicals used per linking sequence is minimized. Similarly, the vibrating and heating of the reaction cell 14 facilitates linkage and permits a reduction in the amount of chemical used over the other known synthesizers as well as overall cycle time. Thus, the present apparatus permits the bio-engineer to efficiently and economically grow any desired oligonucleotide sequences. 
     Before continuing, it should be noted that while parallel coupled syringes of the present type are believed to provide the most efficient delivery mechanism for DNA synthesis, alternatively and for other synthesis activities larger volumes of chemicals may be required. Therefore, it is contemplated that other types of rate controlled pumps could be employed with modification of the present assembly to provide appropriate agitation of the chemicals and sufficient synchronization between the controlled pumps. Further, it is to be recognized that for some applications it may be advantageous to separately control the individual syringes 72 or pumps. 
     Referring now to FIGS. 6 through 10, a more detailed description will follow as to the control circuitry and operation of the present apparatus during its various subroutine sequences. In particular and referring to the hydraulic flow map 32 of FIG. 6, it is to be noted that the flow map 32 is partitioned to shown the previously mentioned chemical groupings and the correlation between the various valve bodies 104, solvent bottles 106, and syringes 72 as well as the points of isolation therebetween. Isolation is required to ensure that the base/reagent/solvents aren&#39;t contaminated with non-compatible base/reagent/solvents prior to delivery to the reaction cell 14. In particular, the valve bodies 104 associated with the solvent bottles 106 are divided into three groups I, II, and III; while the valve bodies 104 associated with the syringes 72 comprise a fourth group IV. Specifically, the valve bodies 104 labeled V11 to V16 and V18 are each associated with one of the solvent bottles 106 of groups I, II and III; while the valve bodies 104 labeled V21 to V25 are each associated with one of the syringes 72 of group IV; and while the valve bodies 104 labeled V17, V26 and V27 control the flow of the base/reagent/solvents to the cell 14 and waste. Finally, the valve body 104 labeled V28 controls the air supply to the syringe assembly 18 and regulator screws 52. FIG. 6 thus essentially sets out a hydraulic flow map and the fluid flow path of the chemicals from the valve bodies 104 to the reaction cell 14. 
     Before continuing, it should be recalled that numerous chemistries may be implemented with the present synthesizer, although for purposes of the present description the phosphotriester chemistry has been chosen to hereinafter represent the functions of this instrument. Therefore assuming a configuration operating in response to a controller 12 programmed with the phosphotriester chemistry, the containers or reservoirs 106 associated with the valve bodies V11 to V16 and V18 would each respectively contain zinc bromide (ZnBr 2 ) (or other &#34;trityl&#34; rem oving chemical) methylene chloride (CH 2  Cl 2 ), dimethyl formamide (DMF), acetonitrile, capping reagent No. 1, capping reagent No. 2 and pyridine. The valve bodies V21 to V25 associated with the syringe assembly 18, on the other hand, would each respectively contain MSNT (or other coupling reagent) and the four bases--guanine (G), cytosine (C), adenine (A) and thymine (T)--and each of which bases have been chemically altered to make the bases chemically reactive. Also, it is to be kept in mind that during a typical cycle or sequence of subroutines (each containing a number of steps), the present apparatus as it dispenses the above chemicals generally operates to perform a series of solvent washings with intermediate flushing subroutines so as to: (1) clean the reaction cell 14 and the base-seeded solid support material or resin and prepare it for the addition of the next selected one or more base nucleotides; (2) add an operator selected one or combination of base nucleotides; and (3) perform a series of post addition subroutines (i.e. syringe refresh, pyridine wash/nitrogen blow down, cap and end). Each of the various subroutines for a typical cycle of the phosphotriester chemistry will, however, be described in greater detail hereinafter. 
     From FIG. 6, it generally is to be recognized that as the various valve bodies 104 are enabled, the liquid flow paths from groups I, II, III and IV all converge at valve body V17. Prior thereto, however, each of the groups are coupled together via appropriate manifold assemblies M1, M2, M3 and M4. Manifolds M1 and M2 are each of a 3×1 configuration, while manifold M3 is of a 2×1 configuration and manifold M4 is of a 6×1 configuration. Each of the manifold assemblies thus accommodates a number of chemical inputs which are coupled via independent flow paths to a common point so as to provide a single output. It is to be recalled that chemical and gaseous isolation is desired between various of the groups so as to prevent intergroup contamination and this is achieved via the various manifold assemblies. In particular, the outputs of manifold M1 and M2 are coupled to a third manifold assembly M3 such that due to the equalized nitrogen pressure of the system on each of the manifold inputs, the chemicals of group I are isolated from group II. Similarly, the chemicals of groups III and IV are isolated from one another via manifold assembly M4; while groups I and II are isolated from groups III and IV via valve body V17. It is to be recognized, though, that while manifold assembies are used in the present embodiment, additional valve bodies 104 may be used in lieu of manifold assemblies M1 to M4 to provide chemical isolation, but that such valve bodies 104 would entail some further control. 
     From the above, it should be apparent that further isolation is also achieved via valve body V17 and which essentially acts as a clearing or selector valve for the various solvent bottles 106 of groups I, II and III and the syringes 72 of group IV. That is, upon the enabling of the valve body V17, only one or the desired simultaneous combination of the solvent/reagents from groups I to IV is selected and directed to valve body V26. There, depending upon the position of valve body V26, the liquid is again selectively directed either through reaction cell 14 to valve body V27 and then to collection or waste; or is blocked from flowing through cell 14 and in which case a nitrogen or argon gas purge is directed from the top of the cell 14 and waste is purged from the bottom of the cell 14. In this fashion, valve bodies V17 and V26 provide selective three-way control and ensure that the liquid chemicals generally enter the reaction cell 14 from the bottom and leave from the top so as to further agitate the contents of the reaction cell 14 during normal liquid flow. (Only during a blow-down operation is sequence reversed.) It should also be apparent that via the vibrator 20, no elaborate mechanical linkage is necessary with the present apparatus to agitate the contents of the reaction cell 14. This is not the case, however, with other known equipment which either do not agitate the reaction cell or shake the reaction cell up and down or variously rotate it, as with one known device which alternately turns the cell 180°. 
     As mentioned, the liquid flow paths of the present system are pressurized with chemically inert, dry nitrogen or argon gas that is regulated to approximately 12 to 25 psi. Therefore, as each of the various valve bodies 104 are selected and depending upon the duration of the enabling signal and pressure applied to the reservoir vessel, an appropriate volume of liquid chemical flows in the selected flow path to the reaction cell 14 via valve bodies V17 and V26. As the base/reagent/solvents are flushed from the cell the waste material is then directed via valve body V26 to valve body V27. There, the waste material is either directed to the test collect station 28 or to waste 26. 
     Although, during nitrogen or argon blow-down operations valve V26 stops fluid flow from valve V17 and directs the gas from the top to the bottom of the cell 14, thereby assisting in the washing and drying of the material in cell 14. For automated systems, it is to be noted that an automated test collection stand may be used in conjunction with valve body V27 and which is appropriately enabled at various points in time to advance and collect the backflushed chemicals from valve body V27. Most typically though such collections are taken only during one step for each cycle and which typically is that step following the admitting of the zinc bromide or other detritylating reagent. In this fashion, the operator may, subsequent to a linking sequence, test the various collected samples to determine if appropriate linkings took place and whether the quantity of the grown sequence is sufficient for laboratory use. 
     As mentioned, the present apparatus is preprogrammed with a plurality of subroutines, all of which are operator selectable, for bonding desired bases or combinations thereof during each cycle as per the programmed chemistry. In this regard a portion of the subroutines are directed to the necessary process steps for the programmed chemistry, while the remainder of the subroutines are concerned with the base addition sequences, once the chemistry has been established. While the various subroutines for the phosphotriester chemistry will be discussed in detail hereinafter, for the moment it is to be recognized that once the chemistry has been selected and the associated subroutines defined, the operator thereafter need only program the desired oligonucleotide sequence via a multi-step listing that specifies the various base sequence subroutines to be accessed, since all necessary chemical additions, timing, etc. will thereafter be performed pursuant to the programmed chemistry. During or subsequent to entry, the present apparatus then displays and/or prints the programmed sequence to ensure accuracy, as well as permits the operator to rewrite the programmed sequence via CLEAR and ENTER functions. 
     The specific subroutines that are operator selectable are shown in Table 1 below and primarily consist of the addition of each of the individual bases as well as the addition of a number of combinations of the bases. It is to be recognized though that while only combinations of two bases are shown, additional combinations of 3 and 4 bases may also be programmed into the subroutine listing so as to provide the operator with still further flexibility. Also, should the operator desire to vary the chemistry, then it may be necessary to vary the subroutines so as to account for changes in the reagents/solvents, the sequence for adding same, the timing, etc. 
     
                       TABLE 1______________________________________BASE(s)         ENTRY______________________________________ADENINE (A)     GOSUB 100CYTOSINE (C)    GOSUB 200GUANINE (G)     GOSUB 300THYMINE (T)     GOSUB 400AC              GOSUB 210AG              GOSUB 220AT              GOSUB 230CG              GOSUB 240CT              GOSUB 250GT              GOSUB 260______________________________________ 
    
     With reference to Example 1 (below), an example of a typical sequence might be d(CACGACCCCTCCACGT) and for which the operator enters the following program listing below. Upon entering the desired sequence, the operator directs the apparatus to go to the first step, execute, print and run. The apparatus in response thereto then begin the first cycle or first base addition by proceeding to an initial methylene chloride-isopropyl alcohol (IPA) wash and continues through a series of cycles during which each of the individual bases are added. Upon completing the end routine the apparatus then stops. During the performance of the routine though, the apparatus displays the total time elapsed as well as the time remaining within each of the individual cycles as they progress. 
     
         ______________________________________EXAMPLE 1:STEP       ENTRY      MEANING______________________________________001        GOSUB 200  C002        GOSUB 100  A003        GOSUB 200  C004        GOSUB 300  G005        GOSUB 100  A006        GOSUB 200  C007        GOSUB 200  C008        GOSUB 200  C009        GOSUB 200  C010        GOSUB 400  T011        GOSUB 200  C012        GOSUB 200  C013        GOSUB 100  A014        GOSUB 200  C015        GOSUB 300  G016        GOSUB 400  T017        GOSUB 990  END ROUTINE018        STOP       STOP______________________________________ 
    
     Similarly if the operator desired to program a mixed probe, he/she would again list the individual subroutines, including the desired mixed bases. The apparatus upon detecting the mixed subroutines would then cause proportional amounts of each of the bases to be added to the reaction cell 14 at the specified cycle of the linking sequence. An example of a mixed probe sequence can be seen upon reference to Example 2 below. 
     
         ______________________________________EXAMPLE 2:d(AACTGGTATTACTGGGCG)ACSTEP       ENTRY      MEANING______________________________________001        GOSUB 100  A002        GOSUB 100  A003        GOSUB 200  C004        GOSUB 400  T005        GOSUB 220  G + A006        GOSUB 300  G007        GOSUB 400  T008        GOSUB 100  T009        GOSUB 400  T010        GOSUB 400  T011        GOSUB 100  A012        GOSUB 200  C013        GOSUB 250  T + C014        GOSUB 300  G015        GOSUB 300  G016        GOSUB 300  G017        GOSUB 200  C018        GOSUB 300  G019        GOSUB 990  END ROUTINE020        STOP       STOP______________________________________ 
    
     With the above general programming operation in mind and recognizing that the steps of each base addition subroutine is peculiar to the selected chemistry, attention is now directed to FIG. 7, wherein a general block diagram is shown of the control circuitry for the present apparatus. Such circuitry is generally organized about the process controller 12 (shown in detail in FIG. 8). Peripheral to the controller 12 and associated therewith for facilitating communications are a printer 120, a remote keyboard 122 and a remote display 124. With respect to the programmed operation, a peripheral program store 126, and internal read only memory (ROM) 128 and random access memory (RAM) 130 are provided. With respect to the valve body selection control signals and the displaying thereof, a number of other functional elements are provided and which comprise digital interface 132, air pressure control valve driver 134, flow display 32, zero crossing switch 136, vibrator 135 and a plurality of controlled buses and grouped output ports from the valve driver 134. 
     Referring now to the various functional elements, the remote keyboard 122 and display 124 interact with the process controller 12 so as to permit the operator to enter subroutine sequences similar to the previous example and to view the data entered. Should errors occur during entry, these may be corrected and viewed so as to ensure their accuracy. During the actual processing, the display also serves the additional function of permitting the operator at any given time to visually determine which subroutine is being performed as well as determine the amount of time remaining for that given cycle and the total elapsed time for the sequence in process. A hard copy of the variously displayed data or process information is also available via the printer 120 and which for the preferred embodiment is coupled to the controller 12 at a 600 baud rate. Depending upon the capabilities of the process controller 12, further functional features, such as temperature monitoring, automatic test analysis etc. may be coupled via the processor 12 to the remote display 124 and provide the operator with a real time monitoring capability. 
     Operator entered data, such as the base nucleotide sequence and various operator programmable process parameters (e.g. time, etc.), upon entry are stored in RAM 130, where they are accessed at appropriate times by the controller 12 as it proceeds through the preprogrammed subroutines stored in the program store 126. For the present system, the program store 126 comprises a standard mini-cassette tape deck, which communicates with controller 12 at a 600 baud rate. It should thus be apparent that while the phosphotriester chemistry has presently been selected as an example any chemistry, any of the various other well known chemistries or for that matter operator initiated chemistries can be programmed into program store 126 in a similar fashion. Thus, the present apparatus is adaptable to all known chemistries or operator determined chemistries and operates in general purpose fashion, rather than in the special purpose fashion of heretofore known synthesizers. 
     ROM 128, like RAM 130, is addressable by the process controller 12 and acts to store addressable data, such as various ones of the 16 characters which may be displayed on the remote display 124 or the various control words that are used to selectively actuate the various valve bodies 104 during each cycle. 
     In this latter regard, as each cycle proceeds, the controller 12 outputs serial data via the address/data bus 138 to the digital interface unit 132. A typical data word is 24 bits wide and is comprised of three eight bit segments, since the present microprocessor is an 8 bit microprocessor. It is to be recognized though that various 16 or 32 bit microprocessors will also serve the present function, albeit with greater cost. As each data word is received by the interface 132, the data is latched into six latches of four bits each, prior to being coupled to the valve driver circuitry 134. At the valve driver, depending upon the handwiring of the various bit positions of the data, the data is broken into a number of fields which control various machine functions, depending upon which of the bits are enabled. In particular, the bit fields control the flow display 32 so as to appropriately turn the various back lights on and off, thereby indicating process status to the operator; provide a number of output switch closures, such as for peripheral test equipment; actuate the vibrator 135; and operate the various valve bodies and as well as control other cycle operations assigned to the group 1, 2 and 3 output ports, but which will be described in greater detail hereinafter. 
     Before addressing these latter functions, it is to be noted that the zero cross switch 136 essentially acts to monitor the vibrator-enabling control signals. At the same time it also monitors the AC power signal to the vibrator 135 in order to detect a zero crossing condition (i.e. the point at which the AC voltage signal is zero). Upon concurrently detecting a zero crossing condition and a vibrator enable signal, the zero cross switch 136 enables the vibrator 135. The zero cross switch 136 thus alleviates system noise and minimizes interference which might otherwise occur, since the present vibrator mechanism 135 is of an inductive type and which might otherwise possibly interject noise into the system if switched other than at a zero crossing. 
     With respect to the bit positions or fields for controlling the group 1, 2 and 3 output ports, attention is next directed to Table 2 below and wherein the specific valve and relay assignments for the present apparatus are shown. Thus, depending upon which of the three bit groups at the various ports are selected, various ones of the valve bodies 104 are enabled for appropriate amounts of time during each cycle. It is to be noted that the actual time is monitored by the controller 12 via its internal crystal oscillator and other various well known control circuitry that acts to divide-down the clock frequency and count the divided signals so as to provide the clock signals necessary to show total elapsed time as well as cycle time remaining. 
     
                       TABLE 2______________________________________VALVE AND RELAY ASSIGNMENTSI/OGROUP  PORT       FUNCTION______________________________________1      1          Zinc Bromide--IPA--CH.sub.2 CL.sub.2 Valve1      2          CH.sub.2 CL.sub.2 --IPA Valve1      3          DMF Valve1      4          THF Valve1      5          Capping Reagent #11      6          Capping Reagent #21      7          Reagent Selection Valve1      8          Pyridine Valve2      1          Guanine in Pyridine Syringe/Valve2      2          Cytosine in Pyridine Syringe/Valve2      3          Adenine in Pyridine Syringe/Valve2      4          Thymine in Pyridine Syringe/Valve2      5          MSNT2      6          N.sub.2 Backflush/Solvent Reagent Valve2      7          Waste-Collect Valve2      8          Syringe Up/Syringe Down3      1          Fraction Collector Advance3      2          Not Used3      3          Synthesis Cell Vibrator On/Off3      4          Auxiliary Contact Closure3      5          Cell Temperature Off______________________________________ 
    
     Referring now to FIG. 8, comprised of FIGS. 8a and 8b, a more detailed schematic diagram is shown of the process controller 12 and its manner of interfacing with the various peripheral circuitry previously described with respect to FIG. 7. Central to the process controller 12 is the central processing unit (CPU) 140 and which in the present embodiment is a Fairchild F8 microprocessor. The actual operation of the microprocessor will therefore not be discussed in detail, but if further information is required, attention is directed to various Fairchild product literature as it relates to the Model F8 mircoprocessor. Generally though and for the present apparatus, the microprocess serves to monitor and execute the operator programmed sequence with respect to the chemistry related subroutines stored in program store 126 (and which are written into RAM 140 via the CPU 140, peripheral I/O 152 and UART 142 upon powering up the present apparatus), while timing the various requisite operations. 
     As the CPU 140 performs its timing and data transfer functions, it communicates with the various associated peripheral circuitry via a number of interface units. In particular with respect to the printer 120, the CPU 140 is coupled to a universal asynchronous receiver/transmitter (UART) 142 that is appropriately biased so as to receive low level parallel data from the CPU 140 and couple it serially to the printer 120 at a 600 baud rate, as determined, by 2 the megahertz clock 144. 
     Similarly, the CPU 140 is coupled to the remote keyboard 122 via an 8 bit input bus 146 and 8 bit output bus 148. The keyboard 122, in turn, is configured as a switching matrix so as to produce an 8 bit character representative of each of its keys and which is received and decoded and by the CPU 140. Upon decoding the received data and assuming that the data is to be coupled to the remote display 124, the CPU 140 places the data along with various control and enable signals on data bus 150. The static memory interface (SMI) 157 in response to a position of the control signals establishes a write enable and the address location in the remote display 124 and after which the data is transmitted by buffer 156 to the corresponding addresses in remote display 124. 
     Similarly, during a read operation, when the CPU 140 is reading the preprogrammed subroutines from program store 126 and writing them into RAM 130, it transmits control signals via the I/O unit 152 to the tape player 126 so as to control the operation of the tape player 126 (i.e. stop/run; enable serial I/O; cassette present; fast forward/forward; and reverse). The preprogrammed data is then serially received by the UART 142 from but 154, translated by the UART 142 to parallel and transmitted via but 150 to RAM 130, all under the control of CPU 140. On the other hand and with reference to FIG. 7, if the CPU 140 desires to generate various switch closure enable signals, these are written via the data bus 150, under the control of the CPU 140, and SMI 157 to provide valve control through digital interface 132 to the valve driver 134. It is to be noted though that at present no input switch closure assignments have been established and therefore the I/O unit 156 serves future expansion. 
     Referring next to the circuitry associated with the CPU 140&#39;s interfacing with the ROM 128 and RAM 130, it is to be noted that appropriate address data is coupled to a static memory interface unit 157, where depending upon whether ROM 128 is to be read or RAM 130 is to be read or written, a portion of the address data is decoded via the ROM/RAM decoders 160 and 162 to establish which 1K of the 4K of RAM (130) or 12K of ROM (128) is to be selected. At the same time the remaining 16 bits of the address data are coupled via bus 164 to buffer 166 and from there to the memory address bus 158 and the associated decoders 170, 172 and 174. Under appropriate circumstances, the outputs of decoders 170, 172 and 174 are used to address the display and valve control functions and which at the same time obtain their control signals and from data bus 150 through buffer 156. 
     Otherwise, during the reading or writing of RAM 130 or ROM 128 and after the selection of the proper portion of memory, the address on memory address bus 158 is coupled to the selected memory where that address is read or written. If data is read from the selected address, it is received via input bus 176 and buffered via buffer 178 before being coupled to the CPU 140 by data bus 150. If on the other hand, data was written into the RAM 130, such as operator programmed data, it is conveyed via the data bus 150 to RAM 130 at the address determined in the above fashion. 
     With the earlier mentioned general operation and description of the electro-mechanical apparatus in mind, the particular DNA synthesis program used to perform the phosphotriester chemistry with the present apparatus will now be described. In this regards, attention will be directed from time to time to various tables and representative flow charss shown in FIGS. 9 and 10 for selected portions of the program. Generally though, the present example synthesis program can be seen upon reference to the summary thereof in Table 3 (below) and wherein the various subroutine functions along with their assigned steps are shown. For purposes of description, it is to be noted that this listing can be broken down into those functions related to the operator programming of a desired DNA coupling sequence (001-099); functions for selecting various ones or combinations of the individual bases; functions for adding the selected bases or combinations to the reaction cell with appropriate preparation and washout steps; functions for performing the washing of the reaction cell; and post addition functions for ensuring that the apparatus is ready for the next base addition. 
     
                       TABLE 3______________________________________Phosphotriester MethodDNA SYNTHESIS PROGRAM SUMMARYSTEPS     ROUTINE______________________________________001-099   Reserved for entry of DNA coupling sequence100-104   Add Adenine200-204   Add Cytosine210-214   Couple A &amp; C (Mixed Probe)220-224   Couple A &amp; G (Mixed Probe)230-234   Couple A &amp; T (Mixed Probe)240-244   Couple C &amp; G (Mixed Probe)250-254   Couple C &amp; T (Mixed Probe)260-264   Couple G &amp; T (Mixed Probe)300-304   Add Guanine400-404   Add Thymine500-505   Base addition preparation510-521   CH.sub.2 Cl.sub.2 IPA Wash525-547   Zinc Bromide (ZnBr.sub.2) Wash550-561   Dimethyl Formadine Wash565-575   Pyridine Wash580-594   Final Wash600-616   Adding and Coupling Adenine620-636   Adding and Coupling Cytosine640-656   Adding and Coupling Guanine660-676   Adding and Coupling Thymine680-698   Mixed AC Synthesis Addition700-718   Mixed AG Synthesis Addition720-738   Mixed AT Synthesis Addition740-758   Mixed CG Synthesis Addition760-778   Mixed CT Synthesis Addition780-798   Mixed GT Synthesis Addition950-957   Syringe Refresh960-964   Post reaction Pyridine Wash/N.sub.2 Blowdown970-981   Capping Routine990-993   End Routine______________________________________ 
    
     With the above simplification in mind, attention is directed to Table 4 wherein a detailed listing is shown of the functions performed by the various subroutines. From Table 4, it is to be noted that steps 100 to 104, 200 to 204, 300 to 304, 400 to 404, 210 to 214, 220 to 224, 230 to 234, 240 to 244, 250 to 254 and 260 to 264 essentially rely upon various others of the subroutines for selecting one or more bases, mixing the bases together for a mixed probe, coupling the bases to the nucleotide seeded resin, washing the reaction cell and capping the desired ends of the nucleotide preparatory to the next base addition. Prior to a base addition though, numerous wash and dry operations are performed and which are listed in steps 500 to 594. During the washing steps, the apparatus operates to successively wash the reaction cell with methylene chloride, the zinc bromide detritylating reagent, a DMF wash, a pyridine wash and a THF wash/dry operation. Also, it is to be noted that various of the washing steps are performed more than one time to ensure the removal of all previously admitted chemicals to the reaction cell 14 and thereby proper coupling, upon adding the next volume of base. 
     Upon reference to the various coupling steps, it is to be noted that they each call upon a subroutine for adding a single base or a mixed base (comprised of two or more bases). Such single base additions subroutines are set forth in steps 600 to 616, 620 to 636, 640 to 656 and 660 to 676. The mixed base additions, on the other hand, are set forth in steps 700 to 718, 720 to 738, 740 to 758, 760 to 778 and 780 to 798. 
     Subsequent to each base addition, various post addition steps are performed and which refresh or refill the syringes, perform a pyridine wash and nitrogen blow down of the reaction cell, capping the ends of the nucleotide sequences prior to the addition of the next base and an END subroutine which turns off the vibrator motor, cell temperature controller 34 and resets the elapsed time counter. It is to be noted though that the END routine is used only at the end of the programmed nucleotide sequence, just prior to stopping. 
     For more information with respect to each of the subroutine listings and the various steps performed therein, attention is directed to Table 4 (below) and the rather comprehensive individual subroutine listings. Upon reference thereto, it is to be noted that various ones of the subroutines also provide for operator intervention, whereby the operator may program additional cycles, time variation or volume variation of the various chemicals and reactions for those subroutines. In this way, the operator is able to vary the synthesis reactions as desired. Thus, within the given chemistry, the operator has a wide latitude of discretion via the present general purpose synthesizer. It is again to be recalled too that this latitude is further increased to various other chemistries by merely substituting appropriate programs therefore into the program store 126 and accessing such chemistries in the same fashion as for the present chemistry. 
     
                       TABLE 4______________________________________ SYNTHESIS SUBROUTINE LISTINGBASE COUPLING ROUTINES:STEP     COMMAND       ACTION/MEANING______________________________________COUPLE ADENINE (A)100      GO SUBRTN 500 Base Addition Preparation101      GO SUBRTN 600 Couple A102      GO SUBRTN 960 Pyridine washout103      GO SUBRTN 970 Cap Ends104      RETURN 0      ReturnCOUPLE CYTOSINE (C)200      GO SUBRTN 500 Base Addition Preparation201      GO SUBRTN 620 Couple C202      GO SUBRTN 960 Pyridine washout203      GO SUBRTN 970 Cap Ends204      RETURN 0      ReturnCOUPLE GUANINE (G)300      GO SUBRTN 500 Base Addition Preparation301      GO SUBRTN 640 Couple G302      GO SUBRTN 960 Pyridine washout303      GO SUBRTN 970 Cap Ends304      RETURN 0      ReturnCOUPLE THYMINE (T)400      GO SUBRTN 500 Base Addition Preparation401      GO SUBRTN 660 Couple T402      GO SUBRTN 960 Pyridine washout403      GO SUBRTN 970 Cap Ends404      RETURN 0      ReturnCOUPLE A &amp; C AT SAME POSITION (MIXED PROBE)210      GO SUBRTN 500 Base Addition Preparation211      GO SUBRTN 680 Add mixed A &amp; C212      GO SUBRTN 960 Pyridine washout213      GO SUBRTN 970 Cap Ends214      RETURN 0      Return 0COUPLE A &amp; G AT SAME POSITION (MIXED PROBE)220      GO SUBRTN 500 Base Addition Preparation221      GO SUBRTN 700 Add mixed A &amp; G222      GO SUBRTN 960 Pyridine washout223      GO SUBRTN 970 Cap Ends224      RETURN 0      Return 0COUPLE A &amp; T AT SAME POSITION (MIXED PROBE)230      GO SUBRTN 500 Base Addition Preparation231      GO SUBRTN 720 Add mixed A &amp; T232      GO SUBRTN 960 Pyridine washout233      GO SUBRTN 970 Cap Ends234      RETURN 0      Return 0COUPLE C &amp; G AT SAME POSITION (MIXED PROBE)240      GO SUBRTN 500 Base Addition Preparation241      GO SUBRTN 740 Add mixed C &amp; G242      GO SUBRTN 960 Pyridine washout243      GO SUBRTN 970 Cap Ends244      RETURN 0      Return 0COUPLE C &amp; T AT SAME POSITION (MIXED PROBE)250      GO SUBRTN 500 Base Addition Preparation251      GO SUBRTN 760 Add mixed C &amp; T252      GO SUBRTN 960 Pyridine washout253      GO SUBRTN 970 Cap Ends254      RETURN 0      Return 0COUPLE G &amp; T AT SAME POSITION (MIXED PROBE)260      GO SUBRTN 500 Base Addition Preparation261      GO SUBRTN 780 Add mixed G &amp; T262      GO SUBRTN 960 Pyridine washout263      GO SUBRTN 970 Cap Ends264      RETURN 0      Return 0______________________________________ 
    
     BASE ADDITION PREPARATION ROUTINES; PHOSPHOTRIESTER METHOD 
     This subroutine lines up the subroutines necessary to complete all the steps prior to the addition of the base(s). It makes use of the multiple subroutine capability of the controller and eliminates the necessity of writing all five GO SUBRTN statements in each base coupling sequence. 
     
         ______________________________________STEP   COMMAND       ACTION/MEANING______________________________________500    GO SUBRTN 510 Methylene chloride - IPA wash                (see Step 510)501    GO SUBRTN 525 Zinc bromide (detriylation) step                (see Step 525)502    GO SUBRTN 550 DMF wash (see Step 550)503    GO SUBRTN 565 Pyridine wash (see Step 565)504    GO SUBRTN 580 THF wash/dry (see Step 580)505    RETURN 0      Return from subroutine______________________________________ 
    
     CH 2  Cl 2  -IPA(85:15)WASH 
     This subroutine prewashes the resin with methylene chloride isopropyl alcohol; removes any remaining capping reagent solvents; and preswells the resin for the deblocking step. The subroutine contains three separate wash and nitrogen backflush cycles. 
     
         ______________________________________STEP  COMMAND       PURPOSE______________________________________510   SET LP CNT20003               Do the wash sequence (steps 511-516)               3 times, using counter 2.511   SET CLOSE 12  Turn on valve 12 for               MeCl.sub.2 --IPA wash.512   SET CLOSE 17  Open valve 17 so MeCl.sub.2 -- IPA               can flow to cell.513   INTVL TM 001.00               Allow 1 min. for solvent flow               (adjustable).514   SET CLOSE 26  Shuts off all solvent flow to cell,               N.sub.2 backflush cell.515   INTVL TM 000.20               N.sub.2 backflush for .20 min. (adjustable).516   SET OPEN 26   N.sub.2 backflush OFF, resume solvent               flow to cell.517   INC LP CNT 2519               Add 1 to total in counter 2, when               total reaches number set in Step               100 go to 519, otherwise go to 518.518   GO TO 511     Till loop counter 2 = total set in               step 510, go back to 511 and               repeat sequence.519   SET OPEN 12   Turn off MeCl.sub.2 --IPA valve.520   SET OPEN 17   Turn off reagent selection valve.521   RETURN 0      Return to main program from               subroutine.______________________________________PROGRAMMABLEPARAMETERS:   STEP    ENTRY______________________________________Change # of total cycles         510     Set LP CNT 2XXXX                 XXXX = Count (total cycles)                 Increase or decrease pressure                 on supply vessel, ORChange volume of         513     INTVL TM TTT.TT-increasesolvent per flush cycle                 TTT.TT (time) for moreon supply vessel,     solvent______________________________________ 
    
     ZINC BROMIDE(ZnBr 2 )DETRIYLATION 
     (Other detritylating reagents may be substituted) 
     This subroutine contains several control sequences so as to control the fraction collector advance, the waste-collect valve and cell vibrator. The sequence flushes the cell twice with the zinc bromide solution, collecting each flush in an individual test tube for later spectrophotometric analysis. 
     1. Advance fraction collector 
     2. Waste valve to collect position 
     3. Select reagents and turn on vibrator 
     4. Flow zinc bromide 2 min. 
     5. Stop flow for 2 min. ZnBr 2  Reaction 
     6. Nitrogen backflush cell to test tube 
     7. Two times through MeCl 2  -IPA wash subroutine 
     8. Advance fraction collector 
     9. Do steps 4-7 again 
     10. Return to main program. 
     
         ______________________________________STEP  COMMAND       PURPOSE______________________________________525   SET CLOSE 31  Advance Fraction Collector526   INTVL TM 0000.01               Hold Advance Relay closed               0.01 min.527   SET OPEN 31   Stop fraction collector advance528   SET CLOSE 27  Waste valve to collect position529   SET LP CNT 10002               Do steps 530-545 two times530   SET CLOSE 17  Select the reagents to the cell531   SET CLOSE 33  Turn on the vibrator532   SET CLOSE 11  Turn on ZnBr.sub.2 flor to synthesis               cell533   INTVL TM 002.00               All ZnBr.sub.2 to flow thru cell               2.00 min.534   SET OPEN 11   Stop the flow through the cell535   INTVL TM 002.00               Hold ZnBr.sub.2 Solution in cell for               2 min.536   SET CLOSE 26  Start N.sub.2 backflush of cell537   INTVL TM 000.15               Backflush cell with N.sub.2 for               0.15 min.538   SET OPEN 26   Stop N.sub.2 backflush, ZnBr.sub.2 residue               still in cell539   SET LP CNT 20002               Set up IPA--CH.sub.2 Cl.sub.2 wash for               2 times540   GO SUBRTN 511 Go through IPA--CH.sub.2 Cl.sub.2 wash               2 times, remove ZnBr.sub.2.541   INC LP CNT 1546               Add 1 to total in counter 1, when               total reaches number set in step               529, go to 546, else go to 542.542   SET CLOSE 31  Advance fraction collector543   INTVL TM 000.01               Hold advance relay closed               0.01 min.544   SET OPEN 31   Stop fraction collector advance545   GO TO 530     Till loop count 1 = set count               (step 529) go back to 530, repeat.546   SET OPEN 27   Set waste valve to position547   RETURN 0      Retun from subroutine______________________________________PROGRAMMABLE PARAMETER:                STEP    ENTRY______________________________________Longer contact to advance                526     INTVL TM (TTT.TT)fraction collector   543Time = TTT.TTMore times through ZnBr.sub.2                529     SET LP CNT (1XXXX)wash (or less) XXXX = CountMore CH.sub.2 Cl.sub.2 --IPA washes                539     SET LP CNT (2XXXX)Count = XXXXMore static time for ZnBr.sub.2                535     INTVL TM (TTT.TT)in cell Time = TTT.TTMore N.sub.2 backflush time for                537     INTVL TM (TTT.TT)ZnBr.sub.2 Time =  TTT.TT______________________________________ 
    
     DIMETHYL FORMAMIDE(DMF)WASH 
     This wash removes residual methylene chloride and IPA from the deblocking step. It involves 3 separate washes of the resin and oligonucleotide chain after the deblocking with 3 nitrogen blowdowns of the cell. 
     1. Wash 1 minute with DMF (approximately 3.0 ml) 
     2. Nitrogen backflush 
     3. Repeat 1 &amp; 2 two more times 
     
         ______________________________________STEP  COMMAND       PURPOSE______________________________________550   SET LP CNT 30003               Do steps 55-557 three times551   SET CLOSE 17  Select reagents552   SET CLOSE 13  Select DMF553   INTVL TM 001.00               Allow DMF to flow 1.00 min.554   SET CLOSE 26  N.sub.2 backflush (stops DMF flow)555   INTVL TM 000.50               Allow N.sub.2 .5 min. flow556   SET OPEN 26   Turn off N.sub.2 backflush - DMF               begins flow again.557   INC LP CNT 3559               Add 1 to counter 3. When = to               count set in 550 go to 559,               otherwise go to 558.558   GO TO 551     REPEAT559   SET OPEN 17   Select Syringes560   SET OPEN 13   Turn off DMF561   RETURN 0      Return from subroutine______________________________________PROGRAMMABLE PARAMETER:                STEP    ENTRY______________________________________More (or fewer) times                550     SET LP CNTDMF wash count = XXXX        3XXXXMore DMF Volume (increase                553     INTVL TMpressure) Increase time      TTT.TTTIME = TTT.TTShorter (or longer) N.sub.2                555     INTVL TMblowdown Inc/Dec             TTT.TTTIME = TTT.TT______________________________________ 
    
     PYRIDINE WASH 
     Pyridine is used to watch out the DMF from the previous step. 
     1. Allow pyridine to flow 1.00 min. (3.0 ml) 
     2. Blow pyridine out of cell 
     3. Repeat one time 
     
         ______________________________________STEP  COMMAND       PURPOSE______________________________________565   SET LP CNT 50002               Use loop counter 5 and set for 2               times through loop to step 574566   SET OPEN 17   Select syringes and Pyridine567   SET CLOSE 18  Turn on pyridine flow568   INTVL TM 001.00               Allow to flow 1.0 min.569   SET OPEN 18   Turn off Pyridine570   SET CLOSE 26  Turn on N.sub.2 Backflush571   INTVL TM 000.50               Backflush 30 seconds572   SET OPEN 26   Turn off N.sub.2 Backflush573   INC LP CNT 5575               Add 1 to counter 5. When = to count               set in 565, go to 575, otherwise               574574   GO TO 566     Repeat575   RETURN 0      Return from subroutine______________________________________PROGRAMMABLE PARAMETERS:                STEP    COMMAND______________________________________More time/or less/thru                565     SET LP CNTloop count = XXXX            (5XXXX)More Pyridine per wash                568     INTVL TM(increase pressure or        (TTT.TT)more time)-TTT.TTMore N.sub.2 Backflush Time                571/or less/ Time = TTT.TT______________________________________ 
    
     FINAL WASH 
     This routine is the last wash prior to the addition of the bases. This step removes the pyridine and uses THF as a highly volatile solvent and is easily removed from the resin by a dry nitrogen blowdown and which also effectively allows the resin to be thoroughly dried prior to introduction of the base and MSNT coupling reagent. The reagent and base then well the resin such that the base penetrates all the resin pores available. 
     1. Flow pyridine (3 ml) 1.0 min. (1st time-3 ml may not make it). 
     2. N 2  blowdown. 
     3. Repeat 3 times. 
     4. Three minute blow dry with N 2 . 
     
         ______________________________________STEP  COMMAND       PURPOSE______________________________________580   SET LP CNT 40003               Set up counter 4 for 3 times               through loop to step 588581   SET CLOSE 17  Set reagents582   SET CLOSE 14  Select THF583   INTVL TM 1.00 Flow THF for 1 min.584   SET CLOSE 26  Turn on N.sub.2 Backflush (turns               off THF)585   INTVL TM 000.25               Backflush 15 seconds with N.sub.2586   Set OPEN 26   Turn OFF N.sub.2 Backflush (turns               of THF)587   INC LP CNT 4589               Add 1 to counter 4, when = to               count set in 580, Go To 589,               otherwise 588588   GO TO 581     REPEAT589   SET OPEN 17   Turn off Reagents590   SET OPEN 14   Turn off THF591   SET CLOSE 26  Turn on N.sub.2 Backflush again592   INTVL TM 003.00               Backflush for 3 min. (or till dry)593   SET OPEN 26   Turn off Backflush594   RETURN 0      Return from subroutine______________________________________ 
    
     BASE DISPENSING ROUTINES 
     The following routines are used to dispense the bases and the MSNT in equal volumes into the synthesis cell. Since the mechanism loads all the syringes and dispenses the contents of all the syringes each time a base is needed, the controller selects which syringes will deliver to the cell and which will deliver back to the supply vial. Thus, any combination of syringes may be selected at random under program control to synthesize any possible strand of DNA. 
     The subroutines that follow depend on the proper arrangement of the base vials on the synthesizer. The vial-syringe assignments used for the present program are as follows: 
     
         ______________________________________  Base Vial         Valve No.______________________________________  Guanine         V-21  Cytosine         V-22  Adenine         V-23  Thymine         V-24  MSNT   V-25______________________________________ 
    
     Each subroutine follows the following sequence: 
     1. Pump syringe once and fill 
     2. Select MSNT and Valve(s) to deliver to cell 
     3. Deliver base(s) and MSNT 
     4. Refill syringes 
     5. Discharge 1 syringe load of MSNT to push dead volume to cell 
     6. Add 1 to counter 9. Nine shows the chain length 
     7. Wait 25 minutes for reaction to complete 
     8. Return 
     
         __________________________________________________________________________ADD ADENINESTEP COMMAND   PURPOSE__________________________________________________________________________600  GO SUBRTN 950          Pump syringes once and fill601  SET CLOSE 25          Select MSNT to deliver to cell602  SET CLOSE 23          Select Adenine to deliver to cell603  SET OPEN 28          Drive syringe up604  INTVL TM 000.05          Deliver MSNT 7 Adenine to cell605  SET OPEN 25          Select MSNT syringe to reload from vial606  SET OPEN 23          Select Adenine syringe to reload from vial607  SET CLOSE 28          Draw bases-MSNT from vials to fill syringes608  INTVL TM 000.05          Allow three seconds of fill609  SET CLOSE 25          Select MSNT to push to cell a dead volume610  SET OPEN 28          Deliver MSNT to cell611  INTVL TM 000.05          Allow three seconds to deliver612  SET OPEN 25          MSNT to refill position613  INC LP CNT 9999          Add 1 to counter 9, &#34;dummy-go-to&#34; of 999614  DISP LT CNT 9          Counter 9 now shows total          couplings completed615  INTVL TM 025.00          Wait 25 mins. for reaction to occur616  RETURN 0  Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETERS:              STEP  ENTRY__________________________________________________________________________Syringes need more time              604   INTVL TM (TTT.TT)to load/deliver 608              611More/less reaction time needed.                    INTVL TM (TTT.TT)Time = TTT.TT__________________________________________________________________________ADD CYTOSINESTEP    COMMAND   PURPOSE__________________________________________________________________________620 GO SUBRTN 950         Pump syringes once and fill621 SET CLOSE 25         Select MSNT to deliver to cell622 SET CLOSE 22         Select Cytosine to deliver to cell623 SET OPEN 28         Drive syringe up624 INTVL TM 000.05         Deliver MSNT &amp; Cytosine to cell625 SET OPEN 25         Select MSNT syringe to reload from vial626 SET OPEN 22         Select Cytosine syringe to reload from vial627 SET CLOSE 28         Draw bases-MSNT from vials to fill syringes628 INTVL TM 000.05         Allow three seconds to deliver629 SET CLOSE 25         Select MSNT to push to cell dead volume630 SET OPEN 28         Deliver MSNT to cell631 INTVL TM 000.05         Allow three seconds to deliver632 SET OPEN 25         MSNT to refill position633 INC LP CNT 9999         Add to 1 counter 9, &#34;dummy go-to&#34; 999634 DISP LP CNT 9         Counter 9 now shows total couplings completed635 INTVL TM 025.00         Wait 25 mins. for reaction to occur636 RETURN 0  Return froM subroutine__________________________________________________________________________PROGRAMMABLE PARAMETERS:              STEP  ENTRY__________________________________________________________________________Syringes need more time              624   INTVL TM (TTT.TT)to load/dever 628              631More/less reaction time              635   INTVL TM (TTT.TT)needed. TiME = TTT.TT__________________________________________________________________________ADD GUANINESTEP COMMAND   PURPOSE__________________________________________________________________________640  GO SUBTRN 950          Pump syringes once and fill641  SET CLOSE 25          Select MSNT to deliver to cell642  SET CLOSE 21          Select Guanine to deliver to cell643  SET OPEN 28          Drive syringe up644  INTVL TM 000.05          Deliver MSNT &amp; Guanine to cell645  SET OPEN 25          Select MSNT syringe to reload from vial646  SET OPEN 21          Select Guanine syringe to reoad from vial647  SET CLOSE 28          Draw bases-MSNT from vials to fill syringes648  INTVL TM 000.05          Allow three seconds to fill649  SET CLOSE 25          Select MSNT to push to cell a dead volume650  SET OPEN 28          Deliver MSNT to cell651  INTVL TM 000.05          Allow three seconds to deliver652  SET OPEN 25          MNST to refill position653  INC LP CNT 999          Add 1 to counter 9, &#34;dummy-go-to&#34; of654  DISP LT CNT 9          Counter 9 now shows total couplings          completed655  INVLT TM 025.00          Wait 25 min&#39;s. for reaction to occur656  RETURN 0  Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETER:              STEP  ENTRY__________________________________________________________________________Syringes need more time to              644   INTVL TM (TTT.TT)load/deliver       648              651More/less reaction time              655   INTVL TM (TTT.TT)needed. Time = TTT.TT__________________________________________________________________________ADD THYMINESTEP COMMAND   PURPOSE__________________________________________________________________________660  GO SUBRTN 950          Pump syringes once and fill661  SET CLOSE 25          Select MSNT to deliver to cell662  SET CLOSE 24          Select Thymine to deliver to cell663  SET OPEN 28          Drive syringe up664  INTVL TM 000.05          Deliver MSNT &amp; Thymine to cell665  SET OPEN 25          Select MSNT syringe to relaod from vial666  SET OPEN 24          Select Thymine syringe to reload from vial667  SET CLOSE 28          Draw bases-MSNT from vials to fill syringes668  INTVL TM 000.05          Allow three seconds to fill669  SET CLOSE 25          Select MSNT to push to cell all dead volume670  SET OPEN 28          Deliver MSNT to cell671  INTVL TM 000.05          Allow three seconds to deliver672  SET OPEN 25          MSNT to refill position673  INC LP CBT 9999          Add 1 to counter 9, &#34;dummy-go-to&#34; 999674  DISP LP CNT 9          Counter 9 now shows total couplings completed675  INTVL TM 025.00          Wait 25 mins. for reaction to occur676  RETURN 0  Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETERS:              STEP  ENTRY__________________________________________________________________________Syringes need more time to              664   INTVL TM (TTT.TT)load/deliver       663              671More/less reaction time              675   INTVL TM (TTT.TT)needed. TIME = TTT.TT__________________________________________________________________________ 
    
     MIXED PROBE(Two Base)SYNTHESIS ROUTINES 
     The following subroutines are used to synthesize mixed probes with two bases at a single position. Since the concentration of each individual base falls from 0.1M to 0.667M, a longer time may be necessary for reaction completion. Note that the last (25 min.) time may be changed to accommodate the longer reaction. 
     
         __________________________________________________________________________ADD ACSTEP COMMAND    PURPOSE__________________________________________________________________________680  GO SUBRTN 950           Charge syringes681  SET CLOSE 25           Select MSNT to cell682  SET CLOSE 23           Select Adenine to cell683  SET CLOSE 22           Select Cytosine to cell684  SET OPEN 28           Drive syringe up685  INTVL TM 000.05           Deliver MSNT, Adenine &amp; Cytosine to           synthesis cell686  SET OPEN 25           MSNT syringe to vial687  SET OPEN 23           Adenine syringe to vial688  SET OPEN 22           Cytosine syringe to vial689  SET CLOSE 28           Drive syringe down to refill690  INTVL TM 000.05           Refill all syringes691  SET CLOSE 25           Select MSNT to deliver to cell692  SET OPEN 28           Drive syringes up693  INTVL TM 000.05           Deliver MSNT to cell and clear dead volume694  SET OPEN 25           MSNT syringes selected to vial695  INC LP CNT 9999           Add 1 to loop counter 9696  DISP LT CNT 9           Count in 9 now = total # of couplings697  INTVL TM 025.00           25 min. reaction time (may need altering)698  RETURN 0   Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETERS:              STEP   ENTRY__________________________________________________________________________More syringes fill/discharge              685    INTVL TM (TTT.TT)time               690              693Longer reaction time.              697    INTVL TM (TTT.TT)Time = TTT.TT__________________________________________________________________________ADD A&amp;GSTEP    COMMAND   PROGRAM__________________________________________________________________________700 GO SUBRTN 950         Charge syringes701 SET CLOSE 25         Select MSNT to cell702 SET CLOSE 23         Select Adenine to cell703 SET CLOSE 21         Select Guanine to cell704 SET OPEN 28         Drive syringe up705 INTVL TM 000.05         Deliver MSNT, Adenine &amp; Guanine to         synthesic cell706 SET OPEN 25         Select MSNT from vial707 SET OPEM 23         Select Adenine from vial708 SET OPEN 21         Select Guanine from vial709 SET CLOSE 28         Refill syringes from vials710 INTVL TM 000.05         Allow 3 secs. for refill711 SET CLOSE 25         Select MSNT for push to cell to clear         dead volume712 SET OPEN 28         Drive syringe up713 INTVL TM 000.05         Allow three seconds to deliver MSNT714 SET OPEN 25         Select MSNT vial715 INC LP CNT 9999         Add to counter 9. Count = # of steps         done in sequence.716 DISP LP CNT 9         Display # of steps in the sequence completed717 INTVL TM 025.00         Wait 25.00 minutes for reaction (may need altering)718 RETURN 0  Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETERS:              STEP                  ENTRY__________________________________________________________________________More syringe fill/dischare              705 INTVL TM (TTT.TT)time               710              713Longer reaction time.              717 INTVL TM (TTT.TT)Time = TTT.TT__________________________________________________________________________ADD A&amp;TSTEP    COMMAND   PURPOSE__________________________________________________________________________720 GO SUBRTN 950         Charge syringes721 SET CLOSE 25         Select MSNT to cell722 SET CLOSE 23         Select Adenine to cell723 SET CLOSE 24         Select Thymine to cell724 SET OPEN 28         Drive syringe up725 INTVL TM 000.05         Deliver MSNT, Adenine &amp; Thymine to         synthesis cell726 SET OPEN 25         Select MSNT from vial727 SET OPEN 23         Select Adenine from vial728 SET OPEN 24         Select Thymine from vial729 SET CLOSE 28         Refill syringes from vials730 INTVL TM 000.05         Allow 3 secs. for refill731 SET CLOSE 25         Select MSNT for push to cell to clear dead volume732 SET OPEN 28         Drive syringe up733 INTVL TM 000.05         Allow three seconds to deliver MSNT734 SET OPEN 25         Select MSNT vial735 INC LP CNT 9999         Add 1 to counter 9. Count =  # of steps         done in sequence736 DISP LP CNT 9         Display # steps in sequence completed737 INTVL TM 025.00         Wait 25.00 minutes for reaction, (may need altering)738 RETURN 0  Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETER:              STEP   ENTRY__________________________________________________________________________More syringe fill/discharge              725    INTVL TM (TTT.TT)time               730              733Longer reaction time              737    INTVL TM (TTT.TT)Time = TTT.TT__________________________________________________________________________ADD C&amp;GSTEP COMMAND     PURPOSE__________________________________________________________________________740  GO SUBRTN 950            Charge syringe741  SET CLOSE 25            Select MSNT to cell742  SET CLOSE 22            Select Cytosine to cell743  SET CLOSE 21            Select Guanine to cell744  SET OPEN 28 Drive syringe up745  INTVL TM 000.05            Deliver MSNT, cytosine &amp; guanine to cell746  SET OPEN 25 MSNT syringe to vial747  SET OPEN 22 Cytosine syringe to vial748  SET OPEN 21 Guanine syringe to vial749  SET OPEN 28 Drive syringe down to refill750  INTVL TM 000.05            Refill all syringes751  SET CLOSE 25            Select MSNT to deliver to cell752  SET OPEN 28 Drive syringes up753  INTVL TM 000.05            Deliver MSNT to cell and clear dead volume754  SET OPEN 25 MSNT syringe selected to vial755  INC LP CNT 9999            Add 1 to loop counter 9756  DISP LP CNT Count in 9 now = total # couplings757  INTVL TM 025.00            25 min. reaction time (may need altering)758  RETURN 0    Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETER:              STEP   ENTRY__________________________________________________________________________More syringe fill/discharge              745    INTVL TM (TTT.TT)time               750Longer reaction time              757    INTVL TM (TTT.TT)Time = TTT.TT__________________________________________________________________________ADD C&amp;TSTEP COMMAND    PURPOSE__________________________________________________________________________760  GO SUBRTN 950           Charge syringes761  SET CLOSE 25           Select MSNT to cell762  SET CLOSE 22           Select cytisone to cell763  SET CLOSE 24           Select thymine to cell764  SET OPEN 28           Drive syringe up765  INTVL TM 000.005           Deliver MSNT, Cytosine &amp; Thymine to           synthesis cell766  SET OPEN 25           MSNT syringe to vial767  SET OPEN 22           Cytosine syringe to vial768  SET OPEN 24           Thymine syringe to vial769  SET CLOSE 28           Drive syringe down to refill770  INTVL TM 000.05           Refill all syringes771  SET CLOSE 25           Select MSNT to deliver to cell772  SET OPEN 28           Drive syrings up773  INTVL TM 000.05           Deliver MSNT to cell and clear dead volume774  SET OPEN 25           MSNT syringe selected to vial775  INC LP CNT 9999           Add 1 to loop counter 9776  DISP LP CNT 9           Count in 9 now = total # of couplings777  INTVL TM 025.00           25 min. reaction time (may need altering)778  RETURN 0   Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETERS:              STEP   ENTRY__________________________________________________________________________More syringe fill/discharge              765    INTVL TM (TTT.TT)Time               770              773Longer reaction time.              777    INTVL TM (TTT TT)Time = TTT.TT__________________________________________________________________________ADD G&amp;TSTEP COMMAND    PURPOSE__________________________________________________________________________780  GO SUBTRN 950           Charge syringes781  SET CLOSE 25           Select MSNT to cell782  SET CLOSE 21           Select Guanine to cell783  SET CLOSE 24           Select Thymine to cell784  SET OPEN 26           Drive syringe up785  INTVL TM 000.05           Deliver MSNT, Adenine &amp; Thymine to cell786  SET OPEN 25           Select MSNT from vial787  SET CLOSE 21           Select Guanine from788  SET OPEN 24           Select Thymine from vial789  SET CLOSE 28           Refill syringes from vials790  INTVL TM 000.05           Allow 3 secs. for refill791  SET CLOSE 25           Select MSNT for push to cell to clear           dead volume792  SET OPEN 28           Drive syringe up793  INTVL TM 000.05           Allow three seconds to deliver MSNT794  SET OPEN 25           Select MSNT vial795  INC LP CNT 999           Add 1 to counter 9. Count # of steps done in           sequence796  DISP LP CNT 9           Display # steps in the sequence completed797  INTVL TM 025.00           Wait 25.00 minutes for reaction           (may need altering)798  RETURN 0   Return from subroutine__________________________________________________________________________PROGRAMMABLE PARAMETER:              STEP   ENTRY__________________________________________________________________________More syringe fill/discharge              785    INTVL TM (TTT.TT)time               790              793Longer reaction time.              797    INTVL TM (TTT.TT)Time TTT.TT__________________________________________________________________________ 
    
     SYRINGE REFRESH ROUTINE 
     This subroutine is used to ensure the syringes are primed and that the reagent lines are refreshed from the base and MSNT supply vials. With no valve selected, the syringes merely fill, dispense and fill again from the supply vials. The following sequence is followed in the subroutine: 
     1. Select syringes 
     2. Drive syringes down to fill 
     3. Dispense contents of syringe back to vials 
     4. Fill syringes prior to selecting which to dispense. 
     
         ______________________________________STEP  COMMAND       PURPOSE______________________________________950   SET CLOSE 28  Drive syringe down to fill951   SET OPEN 17   Select syringes to deliver to cell952   INTVL TM 000.05               Wait 3 sec. for syringes to complete               filling953   SET OPEN 28   Drive syringes up - dispense back               to vials954   INTVL TM 000.05               Wait 3 sec. for syringes to dispense955   SET CLOSE 28  Drive syringes down to fill prior               to cell dispense956   INTVL TM 000.05               3 sec. for syringes to fill957   RETURN 0      Return from subroutine______________________________________PROGRAMMABLE PARAMETER:                STEP    COMMAND______________________________________Syringes need more time to                932     INTVL TM                        TTT.TTfill/dispense Time TTT.TT                934                936______________________________________Alternatively the speed adjust on the front of the synthesizer maybe used to increase the fill speed and rate of dispensing of thebases and MSNT.POST REACTION ROUTINES: PHOSPHOTRIESTERMETHOD: PYRIDINE WASH/N.sub.2 BLOWDOWNSTEP  COMMAND       PURPOSE______________________________________960   SET CLOSE 26  Rotate cell flow valve to N.sub.2               blowdown position961   INTVL TM 000.20               Blowdown cell .20 minutes962   SET OPEN 26   Turn off N.sub.2 blowdown963   GO SUBRTN 565 Go through the pyridine wash               subroutine at step 565964   RETURN 0      Return from subroutine______________________________________PROGRAMMABLE PARAMETER:                STEP    COMMAND______________________________________Longer N.sub.2 Blowdown                941     INTVL TMTime                         TTT.TT______________________________________CAPPING ROUTINESTEP  COMMAND       PURPOSE______________________________________970   SET CLOSE 17  Select reagents971   SET CLOSE 15  Select capping reagent #1972   SET CLOSE 16  Select capping reagent #2973   INTVL TM 001.00               Allow one minute of flow974   SET OPEN 15   Turn off capping reagent #1975   SET OPEN 16   Turn off capping reagent #2976   INTVL TM 003.00               Allow 3 minute reaction time977   SET CLOSE 26  Begin N.sub.2 Backflush of Cell978   INTVL TM 000.25               Allow 15 second backflush979   SET OPEN 26   Turn off N.sub.2 Backflush980   PRINT LP CNT 9               Print number of couplings               completed981   RETURN 0      Return from subroutine______________________________________PROGRAMMABLE PARAMETER:                STEP    COMMAND______________________________________More capping solution                953     INTVL TMvolume-flow (3 ml)           001.00More capping time-static                956     INTVL TM                        003.00______________________________________END ROUTINESTEP  COMMAND        PURPOSE______________________________________990   SET OPEN 33    Turn off cell vibrator991   SET CLOSE 35   Turn off cell temperature992   SET LP CNT 99999                Reset counter 9 to zero993   PRINT TIME     Print elapsed time (indicates                completion synthesis program)994   SET CLOCK 000.00                Reset Clock995   RETURN 0       Return from Subroutine______________________________________ 
    
     While Table 4 sets out in great detail each of the various steps performed during each of the various subroutines, attention is also directed to FIGS. 9 and 10 wherein respective flow charts are shown for a typical base delivery and reaction sequence and a typical DMF wash subroutine. Such sequences will be discussed by way of example only, and it is to be recognized that each of the various other subroutines generally proceed in the same fashion as described in Table 4. Before referring thereto though, attention should also be directed to Table 2, since the flow charts of FIGS. 9 and 10 depend upon the I/O assignments previously discussed with respect to FIG. 7. 
     Referring to FIG. 9, a typical base delivery and reaction sequence begins with the application of an appropriate control signal to I/O group 2, port 8 so as to drive the syringes down and thereby refill the syringes 72 from the vials 50. Next, the controller 12 selects which of the syringes are to deliver their contents to the reaction cell 14 by enabling the associated valve bodies 104. For present purposes though, it will be assumed that thymine is being selected. After waiting approximately three seconds for the syringes to fill, the controller disables port 8 of I/O group 2 so as to drive the syringes up and deliver the contents thereof to their associated vials 50. After waiting approximately 3 seconds, the controller again enables port 8 of I/O Group 2 so as to refill each of the syringes 72. It then again waits for approximately three seconds before repeating the same loop to ensure that the syringes are properly filled before continuing on with its base delivery. It is to be noted that, depending upon the volume of base to be delivered, it may take more or less time to ensure the proper filling of the syringes and therefore the operator may also program an appropriate amount of time to ensure the proper filling of the syringes. 
     The controller 12, upon ensuring that the syringes 72 are full, next enables port 5 of I/O group 2, as well as port 4, before it again disables port 8 so as to drive the syringe assembly 18 up and thereby deliver the MSNT and thymine to the reaction cell 14. Depending upon the amount of program time, the actual delivery period will vary, but upon delivering the desired chemicals, the controller deselects the valve bodies 104 at ports 4 and 5 before again reloading all of the syringes 72. The controller then again selects the MSNT valve body 104 of port 5 of I/O group 2 and again enables the syringe assembly so as to deliver a second volume of MSNT to the reaction cell, before again refilling all syringes. The coupling counter is then incremented by one and the count is displayed so as to advise the operator of the addition of one unit of thymine to the growing DNA chain on the seeded resin in the reaction cell 14. Depending upon the programmed reaction time, the controller next waits until this time has elapsed before it returns the operator programmed sequence and calls the next subroutine. During the waiting time, the vibrator motor 135 and temperature controller 34 are enabled for appropriate amounts of time so as to enhance the chemical reaction in the cell 14. 
     Referring next to FIG. 10 and a typcial DMF wash subroutine (which is performed during the base preparation time), the controller 12 upon calling up steps 552 to 564, sets the loop counter for a count of 3 so that the DMF wash will loop or be repeated three times. Next, the controller selects the DMF reagent via ports 3 and 7 of I/O group 1 and permits the DMF to flow for approximately 1 minute or approximately 3 milliliters. Next, the controller closes port 6 of I/O group 2 and admits nitrogen to the flow path and thereby backflushes the reaction cell 14 so as to discharge the DMF remaining in the cell. After approximately a half a minute, the nitrogen is turned off, the loop counter is incremented and the process is repeated. Upon the loop counter reaching a count of 3, which implies the washing of the cell 3 times, the controller exits from the loop and deselects ports 7 and 3 of I/O group 1 so as to deactuate the valve body 104 to the DMF bottle, before executing the Return 0 subroutine. Thereafter, it is to be recalled, that the controller performs a pyridine wash and a THF wash/dry before it proceeds to the next desired base addition subroutine. 
     In a similar fashion, the above apparatus sequentially proceeds through each of the various subroutines dictated by the programmed chemistry and the operator directed base additions and program parameters, until the desired oligonucleotide sequence has been synthesized in the reaction cell 14. At that time, the apparatus shuts off. Intermediate thereto, though, and depending upon any check points or tests that the operator might desire, the apparatus essentially proceeds as described. 
     While the present apparatus has been described with respect to its present preferred implementation and various modifications thereof, it is to be recognized that still other equivalent arrangements may suggest themselves to those of skill in the art. It is therefore contemplated that the present invention as described and as claimed hereinafter should be interpreted to include all such equivalent structures as heretofore contemplated or within the spirit and scope of the following claims.