Different UmuC requirements for generation of different kinds of UV-induced mutations in Escherichia coli

• Published in: Molecular & general genetics Vol. 243; no. 5; p. 584
• Main Authors: Nowicka, A. (Polish Academy of Sciences, Warsaw (Poland). Inst. of Biochemistry. Biophysics,), Kanabus, M, Sledziewska-Gojska, E, Ciesla, Z
• Format: Journal Article
• Language: English
• Published: Germany 03.06.1994
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; DNA Polymerase III - genetics; DNA Replication; DNA, Bacterial - radiation effects; DNA-Directed DNA Polymerase; dnaQ49; ESCHERICHIA COLI; Escherichia coli - genetics; Escherichia coli - radiation effects; Escherichia coli Proteins; Frameshift Mutation; Genes, Bacterial - radiation effects; IRRADIACION ULTRAVIOLETA; IRRADIATION ULTRAVIOLETTE; MUTACION INDUCIDA; MUTANT; Mutant umuC plasmids; MUTANTES; Mutation; MUTATION PROVOQUEE; Operon; PLASMIDE; PLASMIDIOS; Plasmids - radiation effects; Point Mutation; Protein Biosynthesis; PROTEINAS; PROTEINE; SOS Response (Genetics) - radiation effects; Specificity of UV mutagenesis; Suppression, Genetic; Ultraviolet Rays; UmuDC proteins
• ISSN: 0026-8925; 1432-1874
• DOI: 10.1007/BF00284207

An Escherichia coli strain bearing the dnaQ49 mutation, which results in a defective epsilon subunit of DNA polymerase 3, and carrying the lexA71 mutation, which causes derepression of the SOS regulon, is totally unable to maintain high-copy-number plasmids containing the umuDC operon. The strain is also unable to maintain the pAN4 plasmid containing a partial deletion of the umuD gene but retaining the wild-type umuC gene. These results suggest that a high cellular level of UmuC is exceptionally harmful to the defective DNA polymerase 3 of the dnaQ49 mutant. This finding was used as a basis for selection of new plasmid umuC mutants. The properties of two such mutants, bearing the umuC61 or umuC95 mutation, are described in detail. In the umuC122::Tn 5 strain harbouring the mutant plasmids, UV-induced mutagenesis is severely decreased compared to that observed with the parental umuDC(+) plasmid. Interestingly, while the frequency of UV-induced GC to AT transitions is greatly reduced, the frequency of AT to TA transversions is not affected. Both mutant plasmids bear frameshift mutations within the same run of seven A residues present in umuC(+); in umuC61 the run is shortened to six A whereas in umuC95 is lengthened to eight A. In both umuC61 and umuC95 it was found that translation is partially restored to the proper reading frame. Ti is proposed that under conditions of limiting amounts of UmuC, the protein preferentially facilitates processing of only some kinds of UV-induced lesions.