Replication Protein A Interactions with DNA. 1. Functions of the DNA-Binding and Zinc-Finger Domains of the 70-kDa Subunit

Human replication protein A (RPA) is a multiple subunit single-stranded DNA-binding protein that is required for multiple processes in cellular DNA metabolism. This complex, composed of subunits of 70, 32, and 14 kDa, binds to single-stranded DNA (ssDNA) with high affinity and participates in multiple protein-protein interactions. The 70-kDa subunit of RPA is known to be composed of multiple domains: an N-terminal domain that participates in protein interactions, a central DNA-binding domain (composed of two copies of a ssDNA-binding motif), a putative (C-X2-C-X13-C-X2-C) zinc finger, and a C-terminal intersubunit interaction domain. A series of mutant forms of RPA were used to elucidate the roles of these domains in RPA function. The central DNA-binding domain was necessary and sufficient for interactions with ssDNA; however, adjacent sequences, including the zinc-finger domain and part of the N-terminal domain, were needed for optimal ssDNA-binding activity. The role of aromatic residues in RPA-DNA interactions was examined. Mutation of any one of the four aromatic residues shown to interact with ssDNA had minimal effects on RPA activity, indicating that individually these residues are not critical for RPA activity. Mutation of the zinc-finger domain altered the structure of the RPA complex, reduced ssDNA-binding activity, and eliminated activity in DNA replication.