A bipartite interaction with the processivity clamp potentiates Pol IV-mediated TLS.

Processivity clamps mediate polymerase switching for translesion synthesis (TLS). All three TLS polymerases interact with the β processivity clamp through a conserved clamp-binding motif (CBM), which is indispensable for TLS. Notably, Pol IV also makes a unique secondary contact with the clamp through non-CBM residues.

Single strand gap repair: The presynaptic phase plays a pivotal role in modulating lesion tolerance pathways.

During replication, the presence of unrepaired lesions results in the formation of single stranded DNA (ssDNA) gaps that need to be repaired to preserve genome integrity and cell survival. All organisms have evolved two major lesion tolerance pathways to continue replication: Translesion Synthesis (TLS), potentially mutagenic, and Homology Directed Gap Repair (HDGR), that relies on homologous recombination. In Escherichia coli, the RecF pathway repairs such ssDNA gaps by processing them to produce a recombinogenic RecA nucleofilament during the presynaptic phase.

A non-catalytic role of RecBCD in homology directed gap repair and translesion synthesis.

The RecBCD complex is a key factor in DNA metabolism. This protein complex harbors a processive nuclease and two helicases activities that give it the ability to process duplex DNA ends. These enzymatic activities make RecBCD a major player in double strand break repair, conjugational recombination and degradation of linear DNA.

Ethylene oxide and propylene oxide derived N7-alkylguanine adducts are bypassed accurately in vivo.

Adducts formed at the nucleophilic N7 position of guanine are the most abundant lesions produced by alkylating agents such as ethylene oxide (EO) and propylene oxide (PO). In order to investigate the intrinsic mutagenic potential of N7-alkylguanine adducts, we prepared single-stranded DNA probes containing a single well-defined N7-alkylguanine adduct under conditions that minimize the presence of depurinated molecules. Following introduction of these probes into Escherichia coli cells, the effect of the N7-alkylguanine adducts on the efficiency and fidelity of replication was determined.

Chronology in lesion tolerance gives priority to genetic variability.

The encounter of a replication fork with a blocking DNA lesion is a common event that cells need to address properly to preserve genome integrity. Cells possess two main strategies to tolerate unrepaired lesions: potentially mutagenic translesion synthesis (TLS) and nonmutagenic damage avoidance (DA). Little is known about the partitioning between these two strategies.

Monitoring bypass of single replication-blocking lesions by damage avoidance in the Escherichia coli chromosome.

Although most deoxyribonucleic acid (DNA) lesions are accurately repaired before replication, replication across unrepaired lesions is the main source of point mutations. The lesion tolerance processes, which allow damaged DNA to be replicated, entail two branches, error-prone translesion synthesis (TLS) and error-free damage avoidance (DA). While TLS pathways are reasonably well established, DA pathways are poorly understood.

Alkyltransferase-like protein (eATL) prevents mismatch repair-mediated toxicity induced by O6-alkylguanine adducts in Escherichia coli.

O(6)-alkylG adducts are highly mutagenic due to their capacity to efficiently form O(6)-alkylG:T mispairs during replication, thus triggering G→A transitions. Mutagenesis is largely prevented by repair strategies such as reversal by alkyltransferases or excision by nucleotide excision repair (NER). Moreover, methyl-directed mismatch repair (MMR) is known to trigger sensitivity to methylating agents via a mechanism that involves recognition by MutS of the O(6)-mG:T replication intermediates.

Rad8Rad5/Mms2-Ubc13 ubiquitin ligase complex controls translesion synthesis in fission yeast.

Many DNA lesions cause pausing of replication forks at lesion sites; thus, generating gaps in the daughter strands that are filled-in by post-replication repair (PRR) pathways. In Saccharomyces cerevisiae, PRR involves translesion synthesis (TLS) mediated by Poleta or Polzeta, or Rad5-dependent gap filling through a poorly characterized error-free mechanism. We have developed an assay to monitor error-free and mutagenic TLS across single DNA lesions in Schizosaccharomyces pombe.

The alkyltransferase-like ybaZ gene product enhances nucleotide excision repair of O(6)-alkylguanine adducts in E. coli.

O(6)-methylguanine adducts are potent pre-mutagenic lesions owing to their high capacity to direct mis-insertion of thymine when bypassed by replicative DNA polymerases. The strong mutagenic potential of these adducts is prevented by alkyltransferases such as Ada and Ogt in Escherichia coli that transfer the methyl group to one of their cysteine residues. Alkyl residues larger than methyl are generally weak substrates for reversion by alkyltransferases.