1. Department of Biological Sciences and Chemistry, University of Southern California, University Park, Los Angeles, California 90089-2910, USA
2. Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
3. Section on DNA Replication, Repair and Mutagenesis, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-2725, USA

Correspondence to: Myron F. Goodman¹ Correspondence and requests for materials should be addressed to M.F.G. (Email: mgoodman@usc.edu).

Abstract

The DNA polymerase V (pol V) and RecA proteins are essential components of a mutagenic translesion synthesis pathway in Escherichia coli designed 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 -processivity-clamp, occurs only when RecA nucleoprotein filaments assemble or RecA protomers bind on separate single-stranded (ss)DNA molecules in trans. A 3'-proximal RecA filament end on trans DNA is essential for stimulation; however, synthesis is strengthened by further pol V–RecA interactions occurring elsewhere along a trans nucleoprotein filament. We suggest that trans-stimulation of pol V by RecA bound to ssDNA reflects a distinctive regulatory mechanism of mutation that resolves the paradox of RecA filaments assembled in cis on a damaged template strand obstructing translesion DNA synthesis despite the absolute requirement of RecA for SOS mutagenesis.

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