Replication protein A

Replication protein A (RPA) is a protein that binds single-stranded DNA in eukaryotic cells. During DNA replication, RPA prevents single-stranded DNA (ssDNA) from winding back on itself or from forming secondary structures. This keeps DNA unwound for the polymerase to replicate it. RPA also binds to ssDNA during the initial phase of homologous recombination, an important process in DNA repair and prophase I of meiosis. Like its role in DNA replication, this keeps ssDNA from binding to itself (self-complementizing) so that the resulting nucleoprotein filament can then bound by Rad51 and its cofactors.

A bacterial homolog is called single-strand binding protein (SSB).