The Mutagenesis Protein UmuC Is a DNA Polymerase Activated by UmuD′, RecA, and SSB and Is Specialized for Translesion Replication

Replication of DNA lesions leads to the formation of mutations. In Escherichia coli this process is regulated by the SOS stress response, and requires the mutagenesis proteins UmuC and UmuD′. Analysis of translesion replication using a recently reconstituted in vitro system (Reuven, N. B., Tomer, G., and Livneh, Z. (1998) Mol. Cell 2, 191–199) revealed that lesion bypass occurred with a UmuC fusion protein, UmuD′, RecA, and SSB in the absence of added DNA polymerase. Further analysis revealed that UmuC was a DNA polymerase (E. coli DNA polymerase V), with a weak polymerizing activity. Upon addition of UmuD′, RecA, and SSB, the UmuC DNA polymerase was greatly activated, and replicated a synthetic abasic site with great efficiency (45% bypass in 6 min), 10–100-fold higher than E. coli DNA polymerases I, II, or III holoenzyme. Analysis of bypass products revealed insertion of primarily dAMP (69%), and to a lesser degree dGMP (31%) opposite the abasic site. The UmuC104 mutant protein was defective both in lesion bypass and in DNA synthesis. These results indicate that UmuC is a UmuD′-, RecA-, and SSB-activated DNA polymerase, which is specialized for lesion bypass. UmuC is a member of a new family of DNA polymerases which are specialized for lesion bypass, and include the yeast RAD30 and the humanXP-V genes, encoding DNA polymerase η. Replication of DNA lesions leads to the formation of mutations. In Escherichia coli this process is regulated by the SOS stress response, and requires the mutagenesis proteins UmuC and UmuD′. Analysis of translesion replication using a recently reconstituted in vitro system (Reuven, N. B., Tomer, G., and Livneh, Z. (1998) Mol. Cell 2, 191–199) revealed that lesion bypass occurred with a UmuC fusion protein, UmuD′, RecA, and SSB in the absence of added DNA polymerase. Further analysis revealed that UmuC was a DNA polymerase (E. coli DNA polymerase V), with a weak polymerizing activity. Upon addition of UmuD′, RecA, and SSB, the UmuC DNA polymerase was greatly activated, and replicated a synthetic abasic site with great efficiency (45% bypass in 6 min), 10–100-fold higher than E. coli DNA polymerases I, II, or III holoenzyme. Analysis of bypass products revealed insertion of primarily dAMP (69%), and to a lesser degree dGMP (31%) opposite the abasic site. The UmuC104 mutant protein was defective both in lesion bypass and in DNA synthesis. These results indicate that UmuC is a UmuD′-, RecA-, and SSB-activated DNA polymerase, which is specialized for lesion bypass. UmuC is a member of a new family of DNA polymerases which are specialized for lesion bypass, and include the yeast RAD30 and the humanXP-V genes, encoding DNA polymerase η. -II, -III, polymerase I, II, and III, respectively polymerase chain reaction base pair(s) single-stranded dithiothreitol polyacrylamide gel electrophoresis Mutagenesis caused by UV light and by many other DNA damaging agents in Escherichia coli is under control of the SOS response, a highly regulated stress response, which functions to increase cell survival under adverse environmental conditions that cause DNA damage (1Friedberg E.C. Walker G.C. Siede W. DNA Repair and Mutagenesis. ASM Press, Washington, D. C.1995Google Scholar). Genetic analysis has uncovered four genes, whose products are required for SOS mutagenesis. Two of these, DNA polymerase III (pol-III)1 and RecA, participate also in replication and recombination, respectively. The other two, UmuD and UmuC, are specifically required for the mutagenic reaction. It was found that UmuD is processed into a shorter form, UmuD′, which is the form active in SOS mutagenesis (reviewed in Ref.2Walker G.C. Trends Biochem. Sci. 1995; 20: 416-420Abstract Full Text PDF PubMed Scopus (93) Google Scholar). Based on in vivo and in vitro data, UmuD′ and UmuC were thought to be accessory proteins, which assist DNA polymerase III in replicating DNA lesions which usually block replication (2Walker G.C. Trends Biochem. Sci. 1995; 20: 416-420Abstract Full Text PDF PubMed Scopus (93) Google Scholar, 3Banerjee S.K. Christensen R.B. Lawrence C.W. LeClerc J.E. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 8141-8145Crossref PubMed Scopus (196) Google Scholar, 4Rajagopalan M. Lu C. Woodgate R. O'Donnell M. Goodman M. Echols M. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10777-10781Crossref PubMed Scopus (184) Google Scholar, 5Livneh Z. Cohen-Fix O. Skaliter R. Elizur T. CRC Crit. Rev. Biochem. Mol. Biol. 1993; 28: 465-513Crossref PubMed Scopus (105) Google Scholar). According to this mechanism, the mutations occur by misinsertion opposite the DNA lesion by the DNA polymerase, a result of the miscoding nature of most DNA lesions. Recently SOS mutagenesis was reconstituted with purified components in two laboratories (6Tang M. Bruck I. Eritja R. Turner J. Frank E.G. Woodgate R. O'Donnell M. Goodman M.F. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 9755-9760Crossref PubMed Scopus (180) Google Scholar, 7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar). The results, which confirmed an earlier study (4Rajagopalan M. Lu C. Woodgate R. O'Donnell M. Goodman M. Echols M. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10777-10781Crossref PubMed Scopus (184) Google Scholar), provided strong biochemical evidence that SOS mutagenesis occurs by replication through DNA lesions, in a reaction which depends on UmuC, UmuD′, RecA and SSB. Moreover, it was shown that there is a qualitative difference in the specificity of bypass when translesion replication was compared in the absence or presence of SOS proteins. DNA polymerase III holoenzyme bypassed an abasic site via a misalignment mechanism, resulting in skipping over the lesion, and the formation of −1 frameshifts (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar, 8Tomer G. Reuven N.B. Livneh Z. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 14106-14111Crossref PubMed Scopus (24) Google Scholar). In contrast, in the presence of UmuC, UmuD′, RecA, SSB, and pol-III holoenzyme, the abasic site was replicated, with an A usually inserted opposite it (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar). Here we report that in vitro SOS translesion replication occurs in the absence of added DNA polymerase, and that UmuC is a DNA polymerase, which is activated by UmuD′, RecA, and SSB, and performs very effective lesion bypass. UmuD′, UmuD, and the MBP-UmuC fusion protein were overexpressed and purified as described previously (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar). The UmuC was further purified by heparin-Sepharose CL-6B chromatography (Amersham Pharmacia Biotech). A gradient of 80–1000 mm NaCl was used, and UmuC was eluted at 600 mm NaCl. TheumuC104 allele was constructed by PCR-based site-directed mutagenesis, introducing the 720GAT→AAT mutation (9Koch W.H. Ennis D.G. Levine A.S. Woodgate R. Mol. Gen. Genet. 1992; 233: 443-448Crossref PubMed Scopus (33) Google Scholar). Using plasmid pMAC as a template, the 5′-terminal portion ofumuC was amplified using the primers 5′-ATG GGG TAA ACC GGT GGT TGT-3′ (primer 338) and 5′-CTC ATT AAT ACT GTA AAT CTC-3′ (primer 342), and the 3′-terminal portion of umuC was amplified using the primers 5′-CCG GAA TTC TTT ATT TGA CCC TCA GTA AAT C-3′ (primer 131) and 5′-GTA TTA ATG AGG CAT TCT GCG-3′ (primer 341). The resulting fragments (241 and 983 bp, respectively) contained a sequence overlap of 11 nucleotides spanning the umuC104 mutation. The DNA fragments were gel-purified, mixed, and used in a final PCR step with primers 338 and 131 to construct the entire umuC104gene. The PCR product (1214 bp) was cut with AgeI andEcoRI and subcloned into pMAC, which was previously cleaved with the same nucleases. The resulting plasmid was termed pMAC104. The sequence of the umuC104 gene was verified by DNA sequence analysis. The MBP-UmuC104 protein was purified as described for MBP-UmuC. SSB and RecA were purified as described (Refs. 10Lohman T.M. Overman L.B. J. Biol. Chem. 1985; 260: 3594-3603Abstract Full Text PDF PubMed Google Scholar and 11Cox M.M. McEntee K. Lehman I.R. J. Biol. Chem. 1981; 256: 4676-4678Abstract Full Text PDF PubMed Google Scholar, respectively), except that a phosphocellulose purification step was added for RecA. Restriction nucleases, T4 DNA ligase and T4 polynucleotide kinase were from New England Biolabs. T7 gp6 exonuclease was from Amersham Pharmacia Biotech, and Pwo DNA polymerase, polymerase I (pol-I), and exonuclease III were from Roche Molecular Biochemicals. The preparation of the gapped plasmid carrying a site-specific lesion was recently described (8Tomer G. Reuven N.B. Livneh Z. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 14106-14111Crossref PubMed Scopus (24) Google Scholar, 12Tomer G. Livneh Z. Biochemistry. 1999; 38: 5948-5958Crossref PubMed Scopus (30) Google Scholar). Throughout this study we used gapped plasmid GP21, which contained a site-specific synthetic (tetrahydrofuran) abasic site, and a ssDNA region of approximately 350 nucleotides (Fig. 1). The undamaged gapped plasmid (a plasmid with no base lesion) was prepared by nicking plasmid pOC2 (13Cohen-Fix O. Livneh Z. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 3300-3304Crossref PubMed Scopus (32) Google Scholar) with AatII in the presence of 0.1 mg/ml ethidium bromide (14Barzilai R. J. Mol. Biol. 1973; 74: 739-742Crossref PubMed Scopus (26) Google Scholar). The site-specific nicks were converted into gaps using exonuclease III, in a reaction mixture (300 μl) containing 30 μg of FII pOC2 and 300 units of exonuclease III, for 25 min at 37 °C. The size of the gap was deduced to be approximately 350 nucleotides, based on the electrophoretic migration of the DNA after digestion of the ssDNA region with S1 nuclease. The primed and the gapped oligonucleotides were prepared as described previously (15Paz-Elizur T. Takeshita M. Goodman M. O'Donnell M. Livneh Z. J. Biol. Chem. 1996; 271: 24662-24669Abstract Full Text Full Text PDF PubMed Scopus (56) Google Scholar, 16Paz-Elizur T. Takeshita M. Livneh Z. Biochemistry. 1997; 36: 1766-1773Crossref PubMed Scopus (48) Google Scholar). Briefly, a 32P 5′-labeled synthetic 19-mer (5′-TGCTGCAAGGCGATTAAGT-3′) was annealed to the template 5′-GGAAAACCCTGGCGTTAGCCGACTTAATCGCCTTGCAGCA-3′ (40-mer) to generate the primed template. The gapped duplex oligonucleotide was prepared in a similar way, except that an additional oligonucleotide, 16 nucleotides long (5′-AACGCCAGGGTTTTCC-3′) was annealed to the template, such that a duplex with a 5-nucleotides ssDNA gap was formed (Fig. 3).Figure 3DNA polymerase activity of UmuC in the absence of RecA and SSB. The reactions were performed with a primed oligonucleotide, or a gapped duplex oligonucleotide, as described under “Materials and Methods,” with 230 nmMBP-UmuC and 2.5 μm UmuD′. Pol-I (90 nm) was used as a control. The reactions were conducted for 30 min at 37 °C. M-UmuC (HP) is the MBP − UmuC protein purified by an additional heparin-Sepharose column.View Large Image Figure ViewerDownload Hi-res image Download (PPT) The translesion replication reaction was performed as described previously (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar, 8Tomer G. Reuven N.B. Livneh Z. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 14106-14111Crossref PubMed Scopus (24) Google Scholar), with minor changes. The reaction mixture (25 μl) contained 20 mmTris·HCl, pH 7.5, 8 μg/ml bovine serum albumin, 5 mmDTT, 0.1 mm EDTA, 4% glycerol, 1 mm ATP, 10 mm MgCl2, 0.1 mm each of dATP, dGTP, dTTP, and dCTP, 0.1 μg (2 nm) of gapped plasmid, 0.6 μm SSB, 4 μm RecA, 2.5 μmUmuD′ or UmuD, and 10–230 nm MBP-UmuC. Reactions were carried out at 37 °C for the indicated periods of time. Analysis of the bypass products was modified as follows: prior to cleavage the reaction mixture was treated with calf intestine alkaline phosphatase (0.2 units, 1 h, 37 °C), to hydrolyze remaining dNTPs. This step was introduced because some restriction nuclease preparations were contaminated with DNA polymerase. The DNA was then digested withAsp700 (5 units) and MspA1I (5 units) to produce radiolabeled DNA bands which were four nucleotides longer than with the original XmnI/BstXI cleavage (Fig. 1). The DNA samples were fractionated by 15% PAGE-urea, followed by phosphoimager analysis (Fuji BAS 2500). The extent of bypass was calculated by dividing the amount of bypass products by the amount of the extended primers. The specificity of bypass was determined by DNA sequence analysis of bypass products, as described previously (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar). Gap-filling DNA synthesis was performed with unlabeled gapped plasmid pOC2, which contained no nucleotide lesions. The reaction mixture (25 μl) was performed under conditions similar to those of the translesion replication reaction, except that it contained 5 nm gapped plasmid pOC2, 0.1 mm each of dATP, dCTP, and dGTP, 10 μmα-32PdTTP, 0.6 μm SSB, 4.2 μm RecA, 4.8 μm UmuD′, 500 nmfusion UmuC protein, and 8 units/μl of T4 DNA ligase. Reactions were incubated for 5–20 min at 37 °C, after which the reaction products were analyzed by agarose gel electrophoresis followed by phosphoimaging. Primer extension assays by UmuC were performed with32P end-labeled primed oligonucleotide or gapped duplex oligonucleotide. The reaction mixture (25 μl) was similar to that of the translesion replication assay except that oligonucleotide substrates were at 55 nm. The SOS translesion replication reaction that was reconstituted in our laboratory with purified components included a gapped plasmid carrying a site-specific lesion in the ssDNA region, pol-III holoenzyme, a UmuC fusion protein, UmuD′, RecA, and SSB (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar). The substrate used, termed GP21, was a gapped plasmid containing a ssDNA region of ∼350 nucleotides, a synthetic abasic site in the ssDNA region, and an internal radiolabeled phosphate in the primer terminus strand (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar, 8Tomer G. Reuven N.B. Livneh Z. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 14106-14111Crossref PubMed Scopus (24) Google Scholar). A portion of GP21, including the vicinity of the lesion, is shown in Fig. 1 (upper panel). Addition of a DNA polymerase led to extension of the primer up to the lesion, and when lesion bypass occurred, synthesis continued past the lesion. The analysis of replication products was done by cutting the products with restriction nucleasesMspA1I, which cuts four nucleotides upstream to the radiolabel, and Asp700, which cuts downstream to the lesion, followed by urea-PAGE (Fig. 1, upper panel). The products were then visualized by phosphoimaging. In an attempt to define the of this lesion bypass reaction, we 10 of pol-III holoenzyme were required for translesion we found that translesion replication occurred in the absence of added pol-III holoenzyme This that of the components other than pol-III contained DNA polymerase activity. The was UmuC in to UmuD′ it is to be a DNA polymerase Fig. translesion replication by the UmuC fusion protein, in the presence of UmuD′, RecA, and SSB, added DNA polymerase. that lesion bypass occurred with a UmuC as as 10 the presence of a DNA polymerase in the UmuC of replication by the UmuC polymerase was very as indicated by the amount of primer (Fig. 1, panel). it at the lesion. Fig. 1 reactions with DNA be (Fig. 1, was at the abasic site, and bypass was than with a higher of was These results indicate that of the proteins, most UmuC, is a DNA polymerase specialized for translesion The of the proteins to out DNA synthesis on undamaged DNA was by the of radiolabeled into unlabeled gapped plasmid with no lesions. The replication products were fractionated by agarose gel followed by phosphoimaging. Fig. that the proteins DNA synthesis on undamaged the of the DNA polymerase, each of the components was at a and DNA synthesis was in the same be in of each of RecA, SSB, or UmuD′ caused a strong of DNA synthesis. In contrast, of the UmuC fusion protein DNA synthesis (Fig. 2, This that UmuC is a DNA polymerase and that UmuD′, RecA, and SSB cause a strong of activity. In an attempt to the DNA polymerase activity of UmuC, a synthetic oligonucleotide template, primed with a 32P end-labeled 19-mer oligonucleotide was used as a In a gapped duplex oligonucleotide was by an additional oligonucleotide to the same primer template, such that a 5-nucleotides single-stranded gap was formed (Fig. be in Fig. MBP-UmuC a very weak DNA polymerase activity it was on the gapped duplex the MBP-UmuC protein to an additional purification step on a heparin-Sepharose be in Fig. the DNA polymerase activity of this preparation was higher as compared with the preparation activity on the gapped duplex was higher than on the primed template (Fig. UmuD′ the activity of UmuC (Fig. 1, The of UmuC to bypass an abasic site was with the same of which contained a synthetic abasic site in the template strand at 20 (15Paz-Elizur T. Takeshita M. Goodman M. O'Donnell M. Livneh Z. J. Biol. Chem. 1996; 271: 24662-24669Abstract Full Text Full Text PDF PubMed Scopus (56) Google Scholar). It was found that UmuC or with UmuD′, were to bypass the lesion The same result was with the gapped plasmid UmuC is a DNA polymerase, lesion bypass depends on UmuD′, RecA, and SSB. further evidence that UmuC is a DNA polymerase, the UmuC104 mutant protein was overexpressed and This protein a which it by UV light in vivo (9Koch W.H. Ennis D.G. Levine A.S. Woodgate R. Mol. Gen. Genet. 1992; 233: 443-448Crossref PubMed Scopus (33) Google Scholar, G. Mol. Gen. Genet. PubMed Scopus Google Scholar). This mutation is in the which is of UmuC (1Friedberg E.C. Walker G.C. Siede W. DNA Repair and Mutagenesis. ASM Press, Washington, D. C.1995Google Levine A.S. Woodgate R. 1997; PubMed Google Scholar). A of translesion replication activity revealed that the mutant protein was defective in lesion bypass, with in vivo to 4 and and and 10 to 11 and UmuC104 also to the primer (Fig. 6 and and and that is for both polymerase and lesion bypass The specificity of bypass by was by the DNA sequence of the bypass Analysis of 16 revealed that A was most inserted opposite the synthetic abasic site was inserted This specificity is in with the in vivo mutagenic specificity of abasic T. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, C.W. A. S.K. LeClerc J.E. PubMed Scopus Google Scholar, M. W. PubMed Scopus Google Scholar). In addition to the results it was found (1Friedberg E.C. Walker G.C. Siede W. DNA Repair and Mutagenesis. ASM Press, Washington, D. C.1995Google Scholar) the DNA polymerase activity of the UmuC fusion protein was when it was purified from an E. coli the of a of (2Walker G.C. Trends Biochem. Sci. 1995; 20: 416-420Abstract Full Text PDF PubMed Scopus (93) Google Scholar) or pol-III to translesion replication reactions increase lesion in it caused some because of for the terminus results indicate that UmuC is a lesion bypass DNA polymerase whose activity requires UmuD′, RecA, and SSB. The most of the UmuC polymerase, is to the synthetic abasic site with compared with other E. coli DNA polymerases on the same substrate 12Tomer G. Livneh Z. Biochemistry. 1999; 38: 5948-5958Crossref PubMed Scopus (30) Google Scholar, and Fig. are than or in lesion bypass. holoenzyme was effective than in the synthetic abasic site, this bypass a of mutation (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google G. Reuven N.B. Livneh Z. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 14106-14111Crossref PubMed Scopus (24) Google Scholar). In contrast, replicated the lesion, primarily base a of mutation. The of by the UmuC DNA polymerase in the presence of UmuD′, RecA, and SSB is under our reaction as indicated by the amount of primer This indicate that of the UmuC DNA polymerase on DNA a at this we the that the MBP with that SOS lesion bypass required the DNA and the which up for of the accessory of pol-III holoenzyme (6Tang M. Bruck I. Eritja R. Turner J. Frank E.G. Woodgate R. O'Donnell M. Goodman M.F. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 9755-9760Crossref PubMed Scopus (180) Google Scholar). previously indicated that pol-III holoenzyme was required for lesion bypass, which of the of pol-III holoenzyme were (7Reuven N.B. Tomer G. Livneh Z. Mol. Cell. 1998; 2: 191-199Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar). It is from the results that the replication of the abasic site of the of pol-III holoenzyme. pol-III holoenzyme, or at some of with UmuC to increase the efficiency of translesion This for by the of translesion replication or by the extension of products bypassed by the in vivo for pol-III in SOS mutagenesis Mol. Gen. Genet. PubMed Scopus Google Scholar, A. G. M. Mol. Gen. Genet. 1985; PubMed Scopus (26) Google Scholar, Mutagenesis. PubMed Scopus Google Scholar). preparation of this M. Frank E.G. O'Donnell M. Woodgate R. Goodman M.F. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar) that the is a DNA polymerase and termed it DNA polymerase results with those of M. Frank E.G. O'Donnell M. Woodgate R. Goodman M.F. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar) and that UmuC is the DNA polymerase. A difference the two laboratories is in the protein for translesion In our lesion bypass required the UmuC fusion protein, UmuD′, RecA, and SSB, M. Frank E.G. O'Donnell M. Woodgate R. Goodman M.F. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar) in accessory of pol-III holoenzyme, the and the were This difference from the the two (1Friedberg E.C. Walker G.C. Siede W. DNA Repair and Mutagenesis. ASM Press, Washington, D. C.1995Google Scholar) This study used a gapped DNA with a site-specific lesion in the ssDNA region, M. Frank E.G. O'Donnell M. Woodgate R. Goodman M.F. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar) used a ssDNA with the lesion nucleotides from the DNA (2Walker G.C. Trends Biochem. Sci. 1995; 20: 416-420Abstract Full Text PDF PubMed Scopus (93) Google Scholar) used an MBP-UmuC fusion protein and UmuD′, M. Frank E.G. O'Donnell M. Woodgate R. Goodman M.F. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar) used a of Further are to the in the for pol-III accessory proteins in lesion bypass. The UmuC DNA polymerase is of a family of DNA polymerases which in lesion bypass. This the products of and the humanXP-V genes, which DNA polymerase S. 1999; PubMed Scopus Google Scholar, C. R. A. N. M. M. M. S. K. 1999; PubMed Scopus Google Scholar). In the E. coli gene was recently shown to a DNA polymerase (E. coli DNA polymerase J. M. K. T. Mol. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). This gene is a umuC which functions in mutagenesis A. G. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar). The of this of DNA polymerases the of DNA polymerases with specialized are DNA polymerases specialized for for and also for translesion