Abstract:
The present invention provides an isolated circular plasmid of about 2.6 kb derived from a bacterium belonging to the genus Rhodococcus whose restriction sites compises two SacI sites, one BamII site, one PvuI site, one ScaI site, one SphI site and one XhoI site. In addition, the present invention provides an isolated circular plasmid of about 7.6 kb derived from a bacterium belonging to the genus Rhodococcus whose restriction sites compises one SphI site, two KpnI sites, one BglII site, and three SacI sites. The vectors of the invention can be suitable for Rhodococcus hosts and usefull in industry.

Description:
FIELD OF THE INVENTION 
     The present invention relates to novel plasmids, specifically plasmids derived from bacteria belonging to the genus Rhodococcus. 
     BACKGROUND OF THE INVENTION 
     Bacteria belonging to the genus Rhodococcus have been known to hydrate nitrils to amides or acids. Also, certain strains belonging to Rhodococcus rhodochrous have been known to contain a nitril hydration activity. 
     However, vectors suitable for Rhodococcus hosts have not been developed yet and, in reality, few vectors are available from very few sources such as Rhodococcus sp. H13-A (J. Bacteriol., 1988, 170:638-645) to date. To utilize the useful properties of the bacteria, vectors suitable for Rhodococcus hosts and subsequent industrial use have been long awaited. 
     SUMMARY OF THE INVENTION 
     The present inventors have investigated bacteria belonging to Rhodococcus that contain vectors suitable for hosts and industrial use and successfully found circular plasmids suitable as vectors. The present invention provides an isolated circular plasmid of abut 2.6 kb derived from a bacterium belonging to the genus Rhodococcus whose restriction sites compises tow SacI sites, one BamHI site, on PvuI site, one ScaI site, one SphI site and one XhoI site. In addition, the present invention provides an isolated circular plasmid of about 7.0 kb derived from a bacterium belonging to Rhodococcus sp. whose restriction sites compises one SphI site, two KpnI sites, one BglII site, and three SacI sites. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1 shows a restriction map of plasmid pRC001, pRC002, and pRC003. 
     FIG. 2 shows a restriction map of plasmid pRC010. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Novel plasmids, pRC001, pRC002, and pRC003, are derived from Rhodococcus rhodochrous ATCC 4276, ATCC 14349 or ATCC 14348, respectively. A culture of each Rhodococcus rhodochrous (ATCC 4001) (Mar. 1, 1927), R. rhodochrous (ATCC 4276) (Apr. 4, 1928), R. rhodochrous (ATCC 14348) (Jan. 1, 1943), and R. rhodochrous (ATCC 14349) (Jan. 1, 1943), has been deposited with and is publicly available from the American Type Tissue Culture Collection, 12301 Parklawn Drive, Rockville Md. The sizes of the plasmids are all about 2.6 kb. Table 1 shows numbers of restriction sits and sizes of restriction fragments. 
     
                       TABLE 1______________________________________Restriction      Number of          Sizeenzyme     restriction Sites  (kb)______________________________________SacI       2                  2.3, 0.3BamHI      1                  2.6PvuII      1                  2.6ScaI       1                  2.6SphI       1                  2.6XhoI       1                  2.6______________________________________ 
    
     A novel circular plasmid pRC010 is derived from Rhodococcus rhodochrous ATCC 4001. The size of the plasmid is about 7.0 kb. Table 2 shows numbers of restriction sites and sizes of restriction fragments. 
     
                       TABLE 2______________________________________Restriction      Number of        Sizeenzyme     restriction Sites                       (kb)______________________________________SphI       1                7.0KpnI       2                4.0, 3.0Bg1II      2                6.5, 0.5SacI       3                4.2, 2.0, 0.8______________________________________ 
    
     Examples 
     The following examples will further describe the invention. 
     EXAMPLE 1 
     (1) Isolation and Purification of Plasmid 
     Each of Rhodococcus rhodochrous ATCC 4276, ATCC 14349 or ATCC 14348 was grown in 400 ml of a MY medium (0.5% polypepton, 0.3% bactoyeast extract, 0.3% malt extract, 1% glucose). When OD 660  reached 0.15-0.2, 0.5 U/ml of penicillin G was added to the culture. The culture was further incubated until OD 600  of 1.0. After incubation, bacterial cells were harvested by centrifugation, washed with 40 ml of a TES buffer (10 mM Tris-HCl/pH 8, 10 mM NaCl, 1 mM EDTA), and then suspended in 11 ml of a solution containing 50 mM Tris-HCl/pH 8, 12.5% sucrose, 100 mM NaCl, 1 mg/ml of lysozyme. The suspension was incubated with shaking at 37° C. for 3 hours. 0.6 ml of 0.5M EDTA, 2.4 ml of 5M NaCl, and 4.4 ml of 4% SDS/0.7M NaCl were added in the listed order to the bacterial cell lysate. The mixture was gently swirled and placed on ice for 18 hours. After incubation, the mixture was centrifuged at 4° C., at 65,000×g for an hour. After centrifugation, the supernatant was saved and then 4.6 ml of 50% polyethyleneglycol 6,000 was added to the supernatant. The mixture was placed on ice for 3 hours. After incubation, the mixture was centrifuged at 1,000×g for 5 minutes. The supernatant was discarded and the pellet was dissolved in 5 ml of a TES buffer and then 2 ml of a TES buffer containing 7.5 g of cesium chloride and 1.5 mg/ml of ethidium bromide was added to the pellet solution. The mixture was ultracentrifuged at 130,000×g for 42 hours. After ultracentrifugation, the fraction containing plasmids was removed under the UV light. The plasmid fraction was extracted with n-butanol to remove ethidium bromide. After extraction, the plasmid fraction was dialyzed against TE (10 mM Tris-HCl/pH 8, 1 mM EDTA) and then precipitated with ethanol. The plasmid thus obtained was electrophoresed on a 0.7% agarose gel. The gel was stained with ehidium bromide and examined under the UV light. The band containing plasmids was found on the gel. 
     (2) Determination of Molecular Weight of Plasmid 
     Plasmids were electrophoresed along with pUC18 (2.69 kb), pUC 118 (3.16 kb), and pBR322 (4.36 kg) as markers on a 0.7% agarose gel. The sizes of plasmids were all about 2.6 kb. Plasmids were designated as pRC001 (ATCC 427), pRC002 (ATCC 14349) and pRC 003 (ATCC 14384). The parenthesis indicates the ATCC number of the Rhodococcus rhodochrous source. 
     (3) Numbers and Sizes of Restriction Sites of Plasmids 
     Plasmids, pRC001, pRC002 and pRC 003, were digested with various restriction enzymes and restriction fragments were electrophoresed along with markers such as HindIII- and PstI-digested lambda phase DNA on 0.7% agarose gel and 5% acrylamide gel. The results are shown in Table 3. 
     
                       TABLE 3______________________________________Restriction      Number of          Sizeenzyme     restriction Sites  (kb)______________________________________SacI       2                  2.3, 0.3BamHI      1                  2.6PvuII      1                  2.6ScaI       1                  2.6SphI       1                  2.6XhoI       1                  2.6EcoRI      0                  --HindIII    0                  --Kpn1       0                  --______________________________________ 
    
     EXAMPLE 2 
     (1) Isolation and Purification of Plasmid 
     Rhodococcus rhodochrous ATCC 4001 was grown in 400 ml of a MY medium (0.5% polypepton, 0.3% bactoyeast extract, 0.3% malt extract, 1% glucose). When OD 660  reached 0.15-0.2, 0.5 U/ml of penicillin G was added to the culture. The culture was further incubated unitll OD 660  of 1.0. After incubation, bacterial cells were harvested by centrifugation, washed with 40  ml of a TES buffer (10 mM Tris-HCl/pH 8, 10 mM NaCl, 1 mM EDTA), and then suspended in 11 ml of a solution containing 50 mM Tris-HCl/pH 8, 12.5% sucrose, 100 mM NaCl, 1 mg/ml of lysozyme. The suspension was incubated with shaking at 37° C. for 3 hours. 0.6 ml of 0.5M EDTA, 2.4 ml of 5M NaCl, and 4.44 ml of 4% SDS/0.7M lysate. The mixture was gently swirled and placed on ice for 18 hours. After incubation, the mixture was centrifuged at 4° C., at 65,000×g for an hour. After centrifugation, the supernatant was saved and then 4.6 ml of 50% polyethyleneglycol 6,000 was added to the supernatant. The mixture was placed on ice for 3 hours. After incubation, the mixture was centrifuged at 1,000×g for 5 minutes. The supernatant was discarded and the pellet was dissolved in  5 ml of a TES buffer and then 2 ml of a TES buffer containing 7.5 g of cesium chloride and 1.5 mg/ml of ethidium bromide was added to the pellet solution. The mixture was ultracentrifuged at 130,000×g for 42 hours. After ultracentrifugation, the fraction containing plasmids was removed under the UV light. The plasmid fraction was extracted with n-butanol to remove ethidium bromide. After extraction, the plasmid fraction was dialyzed against TE (10 mM Tris-HCl/pH 8, 1 mM EDTA) and the precipitated with ethanol. The plasmid thus obtained was electrophoresed on a 0.7% agarose gel. The gel was stained with ehidium bromide and examined under the UV light. The band containing plasmids was found on the gel. 
     (2) Determination of Molecular Weight of Plasmid 
     Plasmids were electrophoresed along with pUC18 (2.69 kb), pUC 118 (3.16 kb), and pBR322 (4.36 kb) as markers on a 0.7% kb. The plasmid was designated as pRC010 (ATCC 4001). The parenthesis indicates the ATCC number of the Rhodococcus rhodochrous source. 
     (3) Numbers and Sizes of Restriction Sites of Plasmids 
     Plasmid pRC010 was digested with various restriction enzymes and restriction fragments were electrophoresed along with markers such as HindIII- and PstI-digested lambda phase DNA on 0.7% agarose gel and 5% acrylamide gel. The results are shown in Table 4. 
     
                       TABLE 4______________________________________Restriction      Number of        Sizeenzyme     restriction Sites                       (kb)______________________________________SphI       1                7.0KpnI       2                4.0, 3.0Bg1II      2                6.5, 0.5SacI       3                4.2, 2.0, 0.8BamHI      0                --Bc1I       0                --EcoRI      0                --HindIII    0                --ClaI       0                --PvuII      0                --PstI       0                --ScaI       0                --SmaI       0                --______________________________________