Sloppier copier DNA polymerases involved in genome repair

When chromosomal replication is impeded in the presence of DNA damage, memb ers of a newly discovered UmuC/DinB/Rev1/Rad30 superfamily of procaryotic a nd eucaryotic DNA polymerases catalyze translesion synthesis at blocked rep lication forks. Although these polymerases share sequence elements essentia lly unrelated to the standard replication and repair enzymes, some of them (such as the SOS-induced Escherichia coli pol V) catalyze 'error-prone' tra nslesion synthesis leading to large increases in mutation, whereas others ( an example being the Xeroderma pigmentosum variant gene product XPV pol eta ) carry out aberrant, yet nonmutagenic translesion synthesis. Ongoing studi es of these low fidelity polymerases could provide new insights into the me chanism of somatic hypermutation, a key element in the immune response.