The 32- and 14-Kilodalton Subunits of Replication Protein A Are Responsible for Species-Specific Interactions with Single-Stranded DNA

• Published in: Biochemistry (Easton) Vol. 37; no. 36; pp. 12496 - 12506
• Main Authors: Sibenaller, Zita A, Sorensen, Brenda R, Wold, Marc S
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08.09.1998
• Subjects: Binding Sites; DNA Helicases - chemistry; DNA Helicases - genetics; DNA Replication; DNA, Single-Stranded - metabolism; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Holoenzymes - chemistry; Holoenzymes - genetics; Humans; Molecular Weight; Peptide Fragments - chemistry; Protein Binding - genetics; Replication Protein A; Saccharomyces cerevisiae; Saccharomyces cerevisiae - enzymology; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Species Specificity
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi981110+

Replication protein A (RPA) is a multisubunit single-stranded DNA-binding (ssDNA) protein that is required for cellular DNA metabolism. RPA homologues have been identified in all eukaryotes examined. All homologues are heterotrimeric complexes with subunits of ∼70, ∼32, and ∼14 kDa. While RPA homologues are evolutionarily conserved, they are not functionally equivalent. To gain a better understanding of the functional differences between RPA homologues, we analyzed the DNA-binding parameters of RPA from human cells and the budding yeast Saccharomyces cerevisiae (hRPA and scRPA, respectively). Both yeast and human RPA bind ssDNA with high affinity and low cooperativity. However, scRPA has a larger occluded binding site (45 nucleotides versus 34 nucleotides) and a higher affinity for oligothymidine than hRPA. Mutant forms of hRPA and scRPA containing the high-affinity DNA-binding domain from the 70-kDa subunit had nearly identical DNA binding properties. In contrast, subcomplexes of the 32- and 14-kDa subunits from both yeast and human RPA had weak ssDNA binding activity. However, the binding constants for the yeast and human subcomplexes were 3 and greater than 6 orders of magnitude lower than those for the RPA heterotrimer, respectively. We conclude that differences in the activity of the 32- and 14-kDa subunits of RPA are responsible for variations in the ssDNA-binding properties of scRPA and hRPA. These data also indicate that hRPA and scRPA have different modes of binding to ssDNA, which may contribute to the functional disparities between the two proteins.