SUMMARY
Replication protein A (RPA), a major eukaryotic ssDNA-binding protein, is essential for all metabolic processes that involve ssDNA including DNA replication, repair, and damage signaling. Surprisingly, we found here that RPA binds RNA in vitro with high affinity. Using native RIP method, we isolated RNA-RPA complexes from human cells. Furthermore, RPA promotes R-loop formation between RNA and homologous dsDNA. R-loops, the three-stranded nucleic acid structure consisting of an RNA-DNA hybrid and the displaced ssDNA strand, are common in human genome. R-loops may play an important role in transcription-coupled homologous recombination and DNA replication restart. We reconstituted the process of replication restart in vitro using RPA-generated R-loops and human DNA polymerases. These findings indicate that RPA may play a role in RNA metabolism and suggest a mechanism of genome maintenance that depends on RPA and RNA.
