Two types of replication protein A in seed plants.

Replication protein A (RPA), a heterotrimeric protein composed of 70, 32 and 14-kDa subunits, has been shown to be essential for DNA replication, repair, recombination, and transcription. Previously, we found that, in two seed plants, rice and Arabidopsis, there are two different types of RPA70-kDa subunit. Substantial biochemical and genetic characterization of these two subunits, termed OsRPA70a and OsRPA70b or AtRPA70a and AtRPA70b, respectively, is described in this report. Inactivation of AtRPA70a by transfer DNA insertion or RNA interference is lethal, so the complex containing RPA70a may be essential for DNA replication. Transfer DNA insertion and RNAi lines for AtRPA70b are morphologically normal, albeit hypersensitive to certain mutagens, such as UV-B and methyl methanesulfonate, suggesting that RPA70b functions mostly in DNA repair. In two-hybrid, pull-down and coexpression analysis, OsRPA70b was found to interact more selectively than OsRPA70a with OsRPA32. The data suggest that two different types of RPA heterotrimer are present in seed plants, and that there may be additional 32 and 14-kDa subunit homologs that interact with OsRPA70a. Each of the two probable plant RPA complexes may have different roles in DNA metabolism.