Herpes simplex virus 1 single-strand DNA-binding protein (ICP8) will promote homologous pairing and strand transfer.

The herpes simplex virus type 1 encoded ICP8 protein binds single-stranded (ss) DNA and is required for DNA replication in vitro. We have used electron microscopy to examine the ability of ICP8 to promote homologous pairing and strand transfer reactions. Visualization of M13 ssDNA-ICP8 complexes showed that they preferentially bound and enveloped homologous double-stranded (ds) DNA fragments; their deproteinization released ssDNA circles containing dsDNA segments, and an equal number of linear single strands. Optimal transfer required Mg2+ but not nucleoside triphosphates, and showed a fourfold preference for dsDNA fragments with a few bases recessed ends. Gel electrophoretic analysis confirmed the strand transfer activity of ICP8.