Abstract:
A T4 endonuclease V DNA repair enzyme contains an amino acid sequence within its carboxyl terminal region which is involved in dimer specific binding. The region includes polar nonaromatic basic amino acids and aromatic amino acids between amino acid 128 to 137 positions. The specific activity of the enzyme is greatly increased at low salt concentrations when substitutions are made in aromatic amino acids in the carboxy terminal region.

Description:
This invention was made with Government support under ES0409 awarded by the National Institutes of Health. The Government has certain rights in the invention. 
    
    
     This application is a continuation-in-part of application Ser. No. 401,916, filed Sept. 1, 1989, now abandoned. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a DNA repair enzyme, T4 endonuclease V, having a complete specificity for DNA containing either pyrimidine dimers or apurinic/apyrimidinic sites. More specifically, the present invention relates to alterations in the pyrimidine dimer binding domain of the enzyme for increasing its specific activity at low salt concentrations. 
     BACKGROUND OF THE INVENTION 
     The small size of endonuclease V from bacteriophage T4, combined with the relative complexity of the reactions it catalyzes, makes it an interesting and important DNA repair enzyme to be structurally characterized. Among the T-even bacteriophages, T4 has been shown to be approximately twice as resistant to ultraviolet light inactivation as T2 and T6. Luria, S. E. (1947) Reactivation of a Radiated Bacteriophage by Transfer of Self-reproducing Units, Proc. Natl. Acad. Sci. 33, 253-264. Endonuclease V is coded for by the den V gene. Endonuclease V has been shown by biochemical and genetic analysis to possess four distinctly separable activities: (1) a pyrimidine dimer-specific DNA binding activity; (2) a pyrimidine dimer N-glycosylase activity; (3) an apyrimidinic/apurinic (AP)-endonuclease activity which may be manifest at the site of the N-glycosylase event or which may incise DNA at the site of any missing base; and (4) a salt sensitive linear diffusion along double-stranded DNA. 
     Site-directed mutational studies of the carboxyl terminal region of the enzyme support the concept that this part of the enzyme is intimately involved in binding to DNA at the site of the pyrimidine dimer. This carboxy terminal region of endonuclease V is essential for pyrimidine dimer binding. 
     The endonuclease V enzyme has commercial potential for in vivo as well as in vitro studies and uses. Especially for in vitro studies, it is desirable to possess an altered endonuclease V enzyme having increased specific activity thereby requiring less enzyme to provide a predetermined specific activity. 
     The present invention provides a T4 endonuclease V repair enzyme having increased specific activity at low salt concentrations. 
     SUMMARY OF THE INVENTION 
     A T4 endonuclease V DNA repair enzyme contains an amino acid sequence found within the carboxyl terminal portion of the enzyme which is required for pyrimidine dimer specific DNA binding. The region includes polar, nonaromatic amino acids and aromatic amino acids between amino acid 128 to 137 positions. The terminal region of the enzyme includes additional less polar aromatic moieties for increasing the specific activity of the enzyme at low salt concentrations. 
     The invention further provides a method of increasing the specific activity of T4 endonuclease V DNA repair enzyme, the method including the steps of increasing the aromatic composition of the enzyme at the carboxyl terminal region and performing specific nicking assays at low salt concentration. 
    
    
     FIGURES IN THE DRAWINGS 
     Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
     FIG. 1 (A &amp; B) shows colony forming ability of UV-irradiated E.coli cells harboring various denV gene constructs. Cells were grown for 16 hours at 30° C. in Luria broth (LB) containing 100 μg/ml ampicillin (amp). Appropriate dilutions of cells were plated and UV-irradiated on LB-amp plates and incubated at 30° C. for 36 hours. 
     Symbols for Panels A and B: 
     Panel A 
     ∘--AB2480 with pGX2608-16 (wild type denV) 
     •--AB2480 with pGX2608 (starting plasmid with no denV gene) 
     Δ--AB2480 with pGX2608-16 Tyr129→Phe 
     □--AB2480 with pGX2608-16 Tyr129→Trp 
     Panel B 
     ∘--AB2480 with pGX2608-16 (wild type denV) 
     •--AB2480 with pGX2608 (starting plasmid with no denV gene) 
      --AB2480 with pGX2608-16 Tyr129→Stop 
      --AB2480 with pGX2608-16 Tyr129→Ser 
      --AB2480 with pGX2608-16 Tyr129→Frameshift 
     +--AB2480 with pGX2608-16 Tyr129--3 bp Deletion; 
     FIG. 2 (A,B,C) shows pyrimidine dimer-specific nicking activity of T4 endonuclease V mutants under processive nicking conditions.  3  H-pBR322 DNA containing 25 pyrimidine dimers per molecule in 10 mM Tris (pH 8.0), 1 mM EDTA, 10 mM KCl, 10% (v/v) ethylene glycol were reacted with various amounts of wild type and mutant endonuclease V for 60 minutes at 37° C. After terminating the reactions with 1% SDS, DNAs were separated by agarose gel electrophoresis and the amount of DNA in forms I, II and III was determined; 
     Symbols for Panels A, B, C: 
     ∘--wild type T4 endonuclease V 
     Δ--mutant endonuclease V Tyr129→Phe 
     □--mutant endonuclease V Tyr129→Trp 
     Panel A: Percentage of form I DNA remaining 
     Panel B: First-order rate of loss in mass fraction of form I DNA 
     Panel C: Percentage of Form III DNA 
     Panel D: The intracellular accumulation of the following endonuclease V mutants was below the level which could be quantitated accurately by Western blot analysis. Thus sonicated extracts of known concentrations of soluble proteins were tested for pyrimidine dimer-specific nicking activity. 
     •--AB2480 with pGX2608 
      --AB2480 with pGX2608-16 Tyr129→Stop 
      --AB2480 with pGX2608-16 Tyr129→Ser 
      --AB2480 with pGX2608-16 with Tyr129→Frameshift 
     +--AB2480 with pGX2608-16 Tyr129→3 bp Deletion; 
     FIG. 3 (A &amp; B) shows pyrimidine dimer-specific nicking of T4 endonuclease V mutants under distributive nicking assay conditions.  3  H-pBR322 DNA containing 25 pyrimidine dimers per molecule in 10 mM Tris-HCl (pH 8.0), 1 mM EDTA, 100 mM KCl, 10% (v/v) ethylene glycol was reacted with 1.25 ng of wild type and mutant endonuclease V for various times at 37° C. After terminating the reactions by the addition of SDS to 1%, the DNAs were separated by agarose gel electrophoresis and the amount of DNAs in forms I and II was determined. 
     Symbols for Panels A and B: 
     ∘--wild type T4 endonuclease V 
     Δ--endonuclease V Tyr129→Phe 
     □--endonuclease V Tyr129→Trp 
     Panel A: Percentage of form I DNA remaining throughout the time-course nicking reaction. 
     Panel B: First-order rate of loss in the mass fraction of form I DNA; and 
     FIG. 4 (A &amp; B) shows inhibition of complete incision activity of pyrimidine dimers by methoxyamine. 
     Symbols for Panels A and B: 
     ∘--1.25 ng wild type endonuclease V 
     Δ--0.5 ng endonuclease V Tyr129→Phe 
     □--1.25 ng endonuclease V Tyr129→Trp 
     Panel A:  3  H-pBR322 DNA containing 25 pyrimidine dimers per molecule in 10 mM Tris-HCl (pH 8.0), 1 mM EDTA, 100 mM KCl, 10% (v/v) ethylene glycol and +various concentrations of methoxyamine (addition form a 1M methoxyamine-HCl, pH 7.5 stock) were reacted with wild type and mutant endonuclease V for 1 hour at 37° C. After terminating the reactions with the addition of 1% SDS, the DNAs were separated by agarose gel electrophoresis and quantitated. 
     Panel B: Reaction velocity k in the presence of various concentrations of methoxyamine were ##EQU1## 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, a T4 endonuclease V DNA repair enzyme includes an amino acid sequence including a carboxyl terminal region for pyrimidine dimer binding of a specific activity. The sequence of the T4 endonuclease V gene (denV) and coded for amino acids is given in Table 4 (Valerie, K. et al Identification, physical map location, and sequence of the denV gene from bacteriophage T4. Nucleic Acid Res. 12:8085-8096 (1984)). The carboxyl terminal region of the endonuclease V enzymes spans Trp-128 to Tyr-137 (Trp-Tyr-Lys-Tyr-Tyr-Gly-Lys-Ala-Ile-Tyr). The C terminal region of endonuclease V enzyme is capable of binding the kinked, partially single stranded DNA at the site of a pyrimidine dimer. 
     The present invention is based on studies showing the terminal region including substitutions of other less polar aromatic amino acids increases the specific activity of the enzyme at low salt concentrations. More specifically, in accordance with the present invention, aromatic amino acid substitutions (Phe 129, Trp 129) for a more polar aromatic amino acid (Tyr 129) at the terminal region increases the specific activity of the endonuclease enzyme. 
     In accordance with the following experimental evidence, mutant enzymes including substitutions Tyr-129→Phe (Sequence ID Nos. 1 and 2) and Tyr-129→Trp (Sequence ID Nos. 3 and 4) displayed a 1000% and 500% enhanced specific nicking activity respectively. These reactions were also shown to be completely processive. Assays performed at higher (100 mM) salt concentrations reduced the specific activities of the mutant enzymes approximately to that of the wild type enzyme for the Tyr-129→Phe mutant and 20% of that of the wild type for Tyr-129→Trp mutant as opposed to the activity of the mutant enzymes at lower salt concentrations below 25 mM. The specific activity of the mutant enzyme decreased approximately ten fold when assayed at physiological salt concentrations. 
     The following experimental evidence demonstrates the unexpected increase of activity of the enzyme used in accordance with the present invention. 
     A. EXPERIMENTATION 
     1. Materials and Methods 
     Bacteria, Phage and Plasmids 
     The E.coli strains, M13 phage constructs, T4 phage and plasmids which were utilized in this study are described in Table I. 
     Oligonucleotide Site-directed Mutagenesis 
     The construction of mutant den V genes was performed in M13 O L  P R  den V by standard procedures. All oligonucleotides were synthesized on a Biosearch Cyclone™ and purified as previously described. All mutants were verified by dideoxy sequencing methods. The den V structural gene was subcloned into pGX2608 as described in Recinos, A., III, Augustine, M. L., Higgins, K. M., Lloyd, R. S. &#34;Expression of the bacteriophage T4 denV structural gene in Escherichia coli&#34; J. Bacteriol. 168:1014-1018, 1986; Recinos, A. III, Lloyd, R. S. &#34;Site-directed mutagenesis of the T4 endonuclease V gene: role of lysine-130.&#34;Biochemistry 27:1832-1838, 1988. 
     UV Survival of Bacteria and Complementation of T4 den V1 Phage 
     The procedures to asses UV survival of bacterial cultures and the complementation of UV-irradiated T4 denV1 phage as described in Recinos, A. III, Augustine, M. L. et al supra; Recinos, A. III, Lloyd, R. S. supra. 
     Purification of Mutant T4 Endonuclease V 
     Following the site-directed mutagenesis, sequencing and subcloning of the mutant den V genes into pGX2608, the mutant endonuclease V proteins were expressed off of the O L  P R  hybrid promoter in E. coli AB2480 grown in 30° C. for 16 hours. Cells (100 ml) were pelleted by centrifugation at 4,500×g and resuspended in 10 ml cold 10 mM Tris-HCl (pH8.0), 1 mM EDTA, 100 mM KCl, 10% (v/v) ethylene glycol (Buffer A). Cells were disrupted by sonication and the cell debris removed by centrifugation at 10,000×g. The endonuclease V was batch absorbed for 16 hours at 4° C. onto 3 ml of single-stranded DNA agarose matrix. The single-stranded DNA agarose was pelleted by centrifugation at 1,000×g and the supernatant removed. The agarose matrix was washed 3 times, 10 ml each with Buffer A in order to remove any nonspecific proteins. The endonuclease V was eluted from the washed pellet by resuspending the pellet in buffer A containing 1M KCl. The amount of endonuclease V which was recovered by this procedure was determined by quantitative Western blot analyses in which pure endonuclease V was used to generate a standard curve. 
     Pyrimidine Dimer-specific Plasmid DNA Nicking Assay 
     The ability of the wild type and mutant endonuclease V molecules to produce single-strand breaks in UV-irradiated supercoiled covalently closed circular plasmid DNA (form I) was performed as follows. 
       3  H-pBR322 (1 μg/assay point) was UV-irradiated to produce approximately 25 pyrimidine dimers per DNA molecule. This DNA, in either 10 mM Tris-HCl (pH8.0), 1 mM EDTA, 10 mM KCl, 10% (v/v) ethylene glycol or the same as above except 100 mM KCl, was incubated either with varying concentrations of endonuclease V or with a known concentration of enzyme for increasing amounts of time. Reactions were terminated by the addition of an equal volume of 50 mM Tris-HCl (pH8.0) 10 mM EDTA, 2% SDS, 20% (w/v) sucrose and 0.025% (w/v) bromphenol blue. 
     Nicking assays which measured the inhibition of only the phosphodiester bond scission were performed in either 20 mM Tris-HCl (pH 8.0), 1 mM EDTA, 100 mM KCl, 10% (v/V) ethylene glycol and various concentrations of methoxyamine. Reactions were terminated as described above. The plasmid DNA reaction products were separated by agarose gel electrophoresis and after the DNAs were visualized by ethidium bromide staining, the individual bands were excised from the gel and quantitated as previously described. 
     RESULTS 
     UV Survival of DNA Repair-deficient Cells Harboring Mutant denV Genes 
     The technique of oligonucleotide site-directed mutagenesis was used to create a series of mutations within the T4 denV gene which had been previously subcloned into M13mp18. The mutated genes, which are categorized in Table I, were identified and purified by differential hybridization and verified by dideoxy sequencing techniques. The altered denV structural genes were then excised by ClaI digestion from M13 RF and subcloned into pGX2608, an expression vector which contains a unique ClaI site downstream of hybrid 2 promoter O L  P R . Plasmids were transformed into E.coli AB2480 (uvrA-recA-) and the correct orientation of the denV gene relative to the promoter was verified by restriction enzyme analyses. Individual colonies were grown at 30° C. and tested as to whether the mutant endonuclease V enzymes were capable of conferring enhanced UV resistance to excision-and recombination-deficient E.coli (FIG. 1). As previously demonstrated, the expression of wild type endonuclease V (open circles) in these cells results in a significant enhancement in UV survival relative to that of cells which only harbor the parental vector PGX2608 (Closed circles). FIG. 1, Panel A shows that the substitutions of Tyr129→Trp (□) and Tyr 129→Phe (Δ) in accordance with the present invention produce enzymes whose phenotypic expression only results in approximately one-half the survival enhancement as compared to wild type. UV survival data for all other changes at the Tyr129 position (Ser, stop codon, deletion and frameshift) resulted in UV survivals which were indistinguishable from denV gene being absent from these cells (FIG. 1, Panel B). These data, coupled with previous findings suggest that there is a strong requirement for an aromatic amino acid at this position within the enzyme and these in vivo analyses would suggest that the native tyrosine at position 129 is best suited for conferring resistance to the killing effects of UV. 
     Complementation of the T4 denV1 Phage 
     The cytosine bases within the genome of bacteriophage T4 DNA are modified to glucosylated-5-hydroxymethyl cytosine. It is probably this modification of its DNA which renders the normal E.coli DNA repair enzyme systems unable to initiate repair on damaged UV-irradiated T4 DNA. However, if UV-irradiated T4 denV1 phage infect E.coli cell which contains functional endonuclease V, survival is enhanced. Therefore E.coli harboring each of the mutant T4 endonuclease V constructions were infected with the T4 denV1 phage which had previously been, exposed to various UV dosages. The data summarizing UV dosages required to reduce the phage survival to 10% (D 10 ) are presented in Table II. These data demonstrate that the only two mutants which were capable of enhancing phage survival were the Tyr129→Trp and Tyr129→Phe of the present invention. These data are in good agreement with the UV survival as measured by colony forming ability. The degree of enhanced phage survival closely parallel that observed for cell survival. 
     Pyrimidine Dimer-specific Nicking Activity Assays 
     The wild type endonuclease V locates dimers within DNA through a one-dimensional diffusion mechanism along DNA both in vivo and in vitro at monovalent salt concentrations below 40 mM. In vitro location of dimers and subsequent incision reactions above 40 mM salt proceed by way of a 3-dimensional search through the reaction medium. In order to evaluate the dimer-specific nicking activity of the mutant enzymes of the present invention relative to wild type, E. coli AB2480 harboring various mutant denV expression plasmids were grown and the enzymes were partially purified (to approximately a 10% purity). Whenever possible, the amount of enzyme was determined by quantitative Western blot analyses as previously described. Two of the mutant proteins, Tyr129→Trp and Tyr129→Phe accumulated to levels approximately 100% and 20%, respectively of those found for wild type enzyme (data not shown). 
     Although both sets of in vivo data, presented in FIG. 1 and Table II, suggested that the Tyr129→Trp and Tyr129→Phe would have much lower specific activities relative to wild type, a pyrimidine dimer-specific nicking assay, carried out under processive enzyme conditions (low salt) suggested that both of these mutants had enhanced specific activities (FIG. 2, Panels A and B). When the rapid loss of UV-irradiated form I DNAs (Panel A) for Tyr129→Phe (Δ) and Tyr129→Trp (□) and wild type (∘) are converted into a relative first-order rate constant (Panel B) the Tyr129→Phe and Tyr129→Trp show a 10- and 5-fold enhanced specific activity respectively over that of wild type. 
     In addition to monitoring the loss of form I DNA, a processive nicking reaction is always characterized by a linear increase in the percentage of form III DNA (full-length linear DNA) as the reaction proceeds. Form III DNA is generated when endonuclease V incises pyrimidine dimers in close proximity and on complementary strands. This is a direct consequence of processive sliding and nicking. The percentage of accumulated form III DNA was measured in the experiment described above (Panel C). The accumulation of form III DNA was linear and significantly more rapid for the two mutants relative to wild type. This correlates well with the enhanced rate of loss of form I DNA in these mutants. Table III relates the percentage of form I DNA remaining with the present form III DNA accumulated. For all data points and for all mutants, a given reduction in form I DNA always generated the same percentage of form III DNA, thus providing that both the Tyr129→Phe and Tyr129→Trp mutants like the wild type, act processively in vitro at low salt concentrations. 
     Thus if mutant endonuclease V molecules are functioning in vivo by a similar processive scanning mechanism to that of the wild type enzyme, these results could suggest that enhanced specific activities do not necessarily correlate with enhanced UV survival. In that scenario, the extremely rapid production of single-strand breaks (and possibly double-strand breaks) by the mutant enzymes may occur too rapidly for the successive steps in the DNA repair mechanism, thus leading to cellular death. The repair of UV-irradiated plasmid DNA occurs in two phases: the rapid processive nicking reaction which was catalyzed by endonuclease V and a slower processive mechanism including repair patch synthesis, ligation and supercoiling. 
     The levels of intracellular accumulation of the remainder of the denV mutants was below the level of detection by Western blot analyses (data not shown). Therefore nicking assays were performed using sonicated cell extracts in which the same total amount of cellular protein were added to the dimer nicking assay (Panel D). Since there was very little activity in these mutant cell extracts relative to AB2480-pGX2608 cell extracts (∘) and since precise enzyme quantitation was not possible, no further analyses were carried out on these mutants. 
     In addition to monitoring the specific activity of the mutant enzymes under processive nicking conditions, experiments were also carried out with a distributive nicking assay in which dimers are located through a 3-dimensional search. A total of 1.25 ng each of wild type (∘), Tyr129→Phe (Δ) and Tyr129→Trp (□) were incubated with UV-irradiated DNA for increasing amounts of time (FIG. 3). In contrast to the results observed under processive nicking conditions, the wild type and Tyr129→Phe appear to have an identical specific activity while Tyr129→Trp was reduced to 20% that of wild type. No form III DNA was produced, in any of these reactions, thus suggesting that at 100 mM salt, all of the enzymes tested were functioning in a distributive manner. These results may suggest that the in vitro data generated under the processive, low-salt conditions reflect a subtle alteration in the 3-dimensional structure of the enzyme at low salt in order to achieve the enhanced specific activities. 
     Inhibition of Phosphodiester Bond Scission at Pyrimidine Dimers with Methoxyamine 
     The rate-limiting step in endonuclease V&#39;s formation of the complete incision in the phosphodiester backbone at the site of a dimer has been proposed to be the phosphodiester bond scission rather than binding or glycosylic bond scission (reviewed by Friedberg, Dodson and Lloyd, McMillan et al, and Liuzzi et al). It has been postulated that the endonuclease must dissociate from the dimer site after making the glycosylic bond scission and reassociate, presumably in a different conformation to catalyze the phosphodiester bond scission. Such a model explains the accumulation of DNA with a high frequency of glycosylic bond scissions and few compete incisions when the reactions are performed at elevated pH. 
     In order to completely uncouple the glycosylase activity from the subsequent phosphodiester bond cleavage, Liuzzi et al demonstrated that the addition of 50 mM methoxyamine to the reaction mixture completely inhibited the phosphodiester bond scission activity but had no effect on the rate of glycosylase activity. Therefore in order to test whether the observed enhanced specific activities are due to a significant increase in the rate of phosphodiester bond scission, the effect of increasing methoxyamine concentrations in the reaction mixtures was measured. Experiments were performed in which the concentration of methoxyamine required to inhibit to 50% the phosphodiester bond scission activity was determined for the wild type and mutant enzymes (FIG. 4). Using limiting amounts of enzyme, the percent of form I DNA was followed as the concentration of methoxyamine was varied over nearly 3 orders of magnitude (FIG. 4, Panel A). The relative velocities of the reactions were calculated and are shown in FIG. 4, Panel B. The 50% methoxyamine-induced inhibition was achieved at 2.5 mM for both wild type and Tyr129→Trp mutant, while 4.0 mM was required for the Tyr129 →Phe mutant. Thus, it appears that if the rate of phosphodiester bond scission is the enhanced activity in these mutants, then the rate of methoxyamine reaction on the sugar is orders of magnitude greater than that of the endonuclease V-catalyzed incision. In these experiments the enhanced specific activity measurements would be masked by the methoxyamine reaction. 
     The above experimental data and discussion shows that the enzymes of the present invention exhibit elevated specific activities when the enzymes are assayed under low salt concentrations. The specific activities of these enzymes decrease approximately 10-fold when assayed at physiological salt concentrations. The results of the in vivo assays which measured the biological impact of the production of the enzymes of the present invention in DNA repair-deficient E. coli are consistent with the hypothesis of the inventor that a too rapid production of single-strand breaks in the cellular DNA may least to cell killing. This temporal uncoupling of the incision step from the subsequent repair synthesis, ligation and supercoiling may be deleterious to survival. The enzymes of the present invention may undergo subtle structural alterations at lower salt concentrations which in turn reflect elevated specific activities. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
     
                                           TABLE I__________________________________________________________________________E. coli, Phage and Plasmids Used in this StudyStrain, plasmid or phage             Genotype or phenotype                                 Source__________________________________________________________________________E. coliUT481             met thy Δ(lac-pro) hsdRBamHI hsdM.sup.+                                 C. Lark, U. Utah             supD Tn10/F&#39; traD36 proAB             lacIqZΔ M15AB2480            uvrA6 recA13        A. Ganesan, Stanford U.PlasmidpGX2608           Ap.sup.r λO.sub.L P.sub.R λt.sub.4S             GalK.sup.+          Genex Corp.pGX2608-16-denV.sup.+             Ap.sup.r λO.sub.L P.sub.R endonuclease V.sup.+             λt.sub.4S GalK.sup.+                                 Recinos &amp; Lloyd.sup.20pGX2608-16-denV Tyr129 → Trp             New 129 Codon TGG   This studypGX2608-16-denV Tyr129 → Phe             New 129 Codon TTT   This studypGX2608-16-denV Tyr129 → Stop             New 129 Codon TAA   This studypGX2608-16-denV Tyr129 → Ser             New 129 Codon TCT   This studypGX2608-16-denV Tyr129 →             Codon Deleted at 129                                 This studyDeletionpGX2608-16-denV Tyr129 →             frameshift of 2 bp  This studyFrameshiftPhageM13mp18-O.sub.L P.sub.R denV          Recinos &amp; Lloyd.sup.22M13mp18-O.sub.L P.sub.R denV Tyr129 → Trp                                 This studyM13mp18-O.sub.L P.sub.R denV Tyr129 → Phe                                 This studyM13mp18-O.sub.L P.sub.R denV Tyr129 →                                 This studyStopM13mp18-O.sub.L P.sub.R denV Tyr129 → Ser                                 This studyM13mp18-O.sub.L P.sub.R denV Tyr129 →                                 This studyDeletionM13mp18-O.sub.L P.sub.R denV Tyr129 →                                 This studyFrameshiftwild type T4                          A. Ganesan, Stanford U.T4v1 denV                             A. Ganesan, Stanford__________________________________________________________________________                                 U. 
    
     
                                           TABLE II__________________________________________________________________________Complementation of the Mutant T4 denV1 Phage                               Percent ofE. coli       Phage     D.sub.10                       Survival                               maximal survivalAB2480 cells with plasmids*         T4 WT             T4 denV1                   (J/m.sup.2)                       enhancement                               enhancement**__________________________________________________________________________pGX2608       +         5   1.67    100pGX2608           +     3   1.00    0pGX2608-16(WT +         5   1.67    100endonuclease V)pGX2608-16(WT     +     4.6 1.53    79endonuclease V)pGX2608 Tyr129 → Trp             +     4.5 1.50    75pGX2608 Tyr129 → Phe             +     3.8 1.27    40pGX2608 Tyr129 → Stop             +     3.0 1.00    0pGX2608 Tyr129 → Ser             +     3.0 1.00    0pGX2608 Tyr129 → Deletion             +     3.0 1.00    0__________________________________________________________________________ *Stationary phase E. coli cells were diluted 1:100 into LBamp media and grown at 30° C. until cells were in midlog phase (approximately 5 × 10.sup.8 cells/ml). Various dilutions of irradiated and unirradiated T4 wild type phage and T4 denV1 were mixed with 2.5 × 10.sup.8 cells and plated in 5 ml of 0.7% agarose in LBamp on 25ml 1.5% agar LBamp plates. Phage were grown at 30° for 24 hours.  The UV dose given to the T4 phage which resulted in a 10% plaqueforming ability.  Survival enhancement D.sub.10 /D.sub.10 of T4 denV1 plated on AB2480 pGX2608. **Percent of maximum survival enhancement = (D.sub.10 /D.sub.10 of wild type T4 phage)(100%). 
    
     
                                           TABLE III__________________________________________________________________________Correlation of the Loss of Form I DNA with Accumulation ofForm III DNA-Evidence of Processivity          ln form I ˜0.56          ln form I ˜1.2          ln form I ˜3.2          % form I               % form III                     % form I                          % form III                                % form I                                     % form III__________________________________________________________________________WT endonucleae V          58.3 10.1  31.9 15.5  2.9  32.3endonuclease V Tyr129 → Trp          55.3 10.6  33.1 15.7  5.5  29.8endonuclease V Tyr129 → Phe          56.3  8.9  25.3 18.9  3.8  36.2__________________________________________________________________________ ##STR1## 
    
     
         __________________________________________________________________________SEQUENCE LISTING(1) GENERAL INFORMATION:(iii) NUMBER OF SEQUENCES: 4(2) INFORMATION FOR SEQ ID NO:1:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 417 base pairs(B) TYPE: nucleic acid(C) STRANDEDNESS: single(D) TOPOLOGY: linear(ii) MOLECULE TYPE: DNA (genomic)(iii) HYPOTHETICAL: NO(iv) ANTI-SENSE: NO(ix) FEATURE:(A) NAME/KEY: CDS(B) LOCATION: 1..417(ix) FEATURE:(A) NAME/KEY: mutation(B) LOCATION: replace(386..387, &#34;&#34;)(ix) FEATURE:(A) NAME/KEY: miscfeature(B) LOCATION: 385..387(xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:ATGACTCGTATCAACCTTACTTTAGTATCT GAATTGGCTGACCAACAC48MetThrArgIleAsnLeuThrLeuValSerGluLeuAlaAspGlnHis151015TTAATGGCTGAATATCGTGAATTGCCGCGTG TTTTTGGTGCAGTTCGT96LeuMetAlaGluTyrArgGluLeuProArgValPheGlyAlaValArg202530AAGCATGTTGCTAACGGTAAACGTGTTCGTGATTT TAAAATCAGTCCT144LysHisValAlaAsnGlyLysArgValArgAspPheLysIleSerPro354045ACTTTTATCCTTGGCGCAGGTCATGTTACATTCTTTTACGAT AAGCTC192ThrPheIleLeuGlyAlaGlyHisValThrPhePheTyrAspLysLeu505560GAGTTCTTACGTAAACGTCAAATTGAGCTTATAGCTGAATGTTTAAAA2 40GluPheLeuArgLysArgGlnIleGluLeuIleAlaGluCysLeuLys65707580CGTGGTTTTAATATCAAGGATACTACAGTCCAGGATATTAGTGATATT 288ArgGlyPheAsnIleLysAspThrThrValGlnAspIleSerAspIle859095CCTCAGGAATTCCGTGGTGATTATATTCCCCATGAAGCTTCTATTGCT 336ProGlnGluPheArgGlyAspTyrIleProHisGluAlaSerIleAla100105110ATATCACAAGCTCGTTTAGATGAAAAAATTGCACAACGTCCTACTTGG384 IleSerGlnAlaArgLeuAspGluLysIleAlaGlnArgProThrTrp115120125TTTAAATACTACGGTAAGGCGATTTATGCATAA417PheLys TyrTyrGlyLysAlaIleTyrAla130135(2) INFORMATION FOR SEQ ID NO:2:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 138 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: protein(xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:MetThrArgIleAsnLeuThr LeuValSerGluLeuAlaAspGlnHis151015LeuMetAlaGluTyrArgGluLeuProArgValPheGlyAlaValArg2025 30LysHisValAlaAsnGlyLysArgValArgAspPheLysIleSerPro354045ThrPheIleLeuGlyAlaGlyHisValThrPhePheTyrAspLys Leu505560GluPheLeuArgLysArgGlnIleGluLeuIleAlaGluCysLeuLys65707580ArgGlyPheA snIleLysAspThrThrValGlnAspIleSerAspIle859095ProGlnGluPheArgGlyAspTyrIleProHisGluAlaSerIleAla100 105110IleSerGlnAlaArgLeuAspGluLysIleAlaGlnArgProThrTrp115120125PheLysTyrTyrGlyLysAlaIleTyrAla 130135(2) INFORMATION FOR SEQ ID NO:3:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 417 base pairs(B) TYPE: nucleic acid(C) STRANDEDNESS: single(D) TOPOLOGY: linear(ii) MOLECULE TYPE: DNA (genomic)(ix) FEATURE:(A) NAME/KEY: CDS(B) LOCATION: 1..417(ix) FEATURE: (A) NAME/KEY: mutation(B) LOCATION: replace(386..387, &#34;&#34;)(ix) FEATURE:(A) NAME/KEY: miscfeature(B) LOCATION: 385..387(xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:ATGACTCGTATCAACCTTACTTTAGTATCTGAATTGGCTGACCAACAC48MetThrArgIleAsnLeuThrLeuVa lSerGluLeuAlaAspGlnHis151015TTAATGGCTGAATATCGTGAATTGCCGCGTGTTTTTGGTGCAGTTCGT96LeuMetAlaGluTyrArgGluLeuPro ArgValPheGlyAlaValArg202530AAGCATGTTGCTAACGGTAAACGTGTTCGTGATTTTAAAATCAGTCCT144LysHisValAlaAsnGlyLysArgValArgAs pPheLysIleSerPro354045ACTTTTATCCTTGGCGCAGGTCATGTTACATTCTTTTACGATAAGCTC192ThrPheIleLeuGlyAlaGlyHisValThrPhePheTyr AspLysLeu505560GAGTTCTTACGTAAACGTCAAATTGAGCTTATAGCTGAATGTTTAAAA240GluPheLeuArgLysArgGlnIleGluLeuIleAlaGluCysLeuLys 65707580CGTGGTTTTAATATCAAGGATACTACAGTCCAGGATATTAGTGATATT288ArgGlyPheAsnIleLysAspThrThrValGlnAspIleSerAspIle 859095CCTCAGGAATTCCGTGGTGATTATATTCCCCATGAAGCTTCTATTGCT336ProGlnGluPheArgGlyAspTyrIleProHisGluAlaSerIleAla 100105110ATATCACAAGCTCGTTTAGATGAAAAAATTGCACAACGTCCTACTTGG384IleSerGlnAlaArgLeuAspGluLysIleAlaGlnArgProThrTrp 115120125TGGAAATACTACGGTAAGGCGATTTATGCATAA417TrpLysTyrTyrGlyLysAlaIleTyrAla130135(2) INFORMATION FOR SEQ ID NO:4: (i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 138 amino acids(B) TYPE: amino acid(D) TOPOLOGY: linear(ii) MOLECULE TYPE: protein(xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:MetThrArgIleAsnLeuThrLeuValSerGluLeuAlaAspGlnHis15 1015LeuMetAlaGluTyrArgGluLeuProArgValPheGlyAlaValArg202530LysHisValAlaAsnGlyLysArgValArgAspPheLys IleSerPro354045ThrPheIleLeuGlyAlaGlyHisValThrPhePheTyrAspLysLeu505560GluPheLeuArgLy sArgGlnIleGluLeuIleAlaGluCysLeuLys65707580ArgGlyPheAsnIleLysAspThrThrValGlnAspIleSerAspIle85 9095ProGlnGluPheArgGlyAspTyrIleProHisGluAlaSerIleAla100105110IleSerGlnAlaArgLeuAspGluLysI leAlaGlnArgProThrTrp115120125TrpLysTyrTyrGlyLysAlaIleTyrAla130135