An SOS-regulated operon involved in damage-inducible mutagenesis in Caulobacter crescentus

Abstract

DNA polymerases of the Y-family, such as Escherichia coli UmuC and DinB, are specialized enzymes induced by the SOS response, which bypass lesions allowing the continuation of DNA replication. umuDC orthologs are absent in Caulobacter crescentus and other bacteria, raising the question about the existence of SOS mutagenesis in these organisms. Here, we report that the C.crescentus dinB ortholog is not involved in damage-induced mutagenesis. However, an operon composed of two hypothetical genes and dnaE2, encoding a second copy of the catalytic subunit of Pol III, is damage inducible in a recA-dependent manner, and is responsible for most ultraviolet (UV) and mitomycin C-induced mutations in C.crescentus. The results demonstrate that the three genes are required for the error-prone processing of DNA lesions. The two hypothetical genes were named imuA and imuB, after inducible mutagenesis. ImuB is similar to proteins of the Y-family of polymerases, and possibly cooperates with DnaE2 in lesion bypass. The mutations arising as a consequence of the activity of the imuAB dnaE2 operon are rather unusual for UV irradiation, including G:C to C:G transversions.

Essential roles for imuA ′- and imuB -encoded accessory factors in DnaE2-dependent mutagenesis in Mycobacterium tuberculosis

“…The same phenotype resulted from deletion of imuA′ and was complemented by integration of a wild-type copy of imuA′. These data established the individual essentiality of ImuA′ and ImuB for induced mutagenesis and confirmed the designation of the mycobacterial ImuA′ as a distant homolog of ImuA (5,6). Msm imuA′ and imuB deletion mutants were hypersensitive to mitomycin C (MMC), a genotoxic agent known to induce the SOS response in mycobacteria (1) (Fig.…”

“…S2) and strongly implies that these proteins cannot function as DNA polymerases (22). In turn, this observation suggests a model for translesion synthesis in which DnaE2 itself catalyzes lesion bypass (6).…”

“…Rv3395c homologs are found in a limited number of organisms and their function is unknown, whereas Rv3394c exhibits significant homology to ImuB proteins (6), identifying the Rv3395c-Rv3394c operon as part of a split imuA′-imuB/dnaE2 cassette (5). Rv3394c (ImuB) contains a predicted β-clamp-binding motif, which designates the protein as a DinB3-type Y-family polymerase (11).…”

A plasmid-encoded UmuD homologue regulates expression of Pseudomonas aeruginosa SOS genes

“…These data confirmed that UmuDpR is a transcriptional regulator able to repress the expression of SOS genes. This transcriptional control included the genes encoding RecA and LexA, the main modulators of the SOS response, and the imuA gene, which has been involved in DNA-damage-induced mutagenesis in the alphaproteobacterium Caulobacter crescentus (Galhardo et al, 2005). Transcription of the phl gene, which encodes a photolyase-like enzyme that repairs UV-induced DNA lesions, showed no significant changes in both the lexA 2 mutant and in its umuDpR transformant (Fig.…”

A resposta SOS de Caulobacter crescentus e relações dos mecanismos de reparo com a progressão do ciclo celular.

“…Recently, we have demonstrated that a three-gene operon encoding a hypothetical protein (ImuA), a protein similar to members of the Y family of DNA polymerases (ImuB), and a second copy of dnaE (DnaE2) is responsible for the DNA damage-inducible mutagenesis in Caulobacter crescentus, a function performed by the UmuDC proteins in E. coli. (25). This SOS-regulated operon is widespread in Bacteria (1) and was recently shown to be part of the SOS-mediated response to the antibiotic ciprofloxacin in Pseudomonas aeruginosa (11), demonstrating the relevance of expanding the knowledge about the SOS regulatory circuit in other models.…”