RecA acts in trans to allow replication of damaged DNA by DNA polymerase V

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Abstract

The DNA polymerase V (pol V) and RecA proteins are essential components of a mutagenic translesion synthesis pathway inEscherichia colidesigned to cope with DNA damage. Previously, it has been assumed that RecA binds to the DNA template strand being copied. Here we show, however, that pol-V-catalysed translesion synthesis, in the presence or absence of the β-processivity-clamp, occurs only when RecA nucleoprotein filaments assemble or RecA protomers bind on separate single-stranded (ss)DNA moleculesin trans.A 3′-proximal RecA filament end ontransDNA is essential for stimulation; however, synthesis is strengthened by further pol V-RecA interactions occurring elsewhere along atransnucleoprotein filament. We suggest thattrans-stimulation of pol V by RecA bound to ssDNA reflects a distinctive regulatory mechanism of mutation that resolves the paradox of RecA filaments assembled incison a damaged template strand obstructing translesion DNA synthesis despite the absolute requirement of RecA for SOS mutagenesis.

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