Characterization of physical and functional interactions between eukaryote-like Orc1/Cdc6 proteins and Y-family DNA polymerase in the hyperthermophilic archaeon Sulfolobus solfataricus

The roles of Y-family DNA polymerases and the regulation mechanisms are not well defined in Archaea. In this study, we performed in vitro and in vivo characterization of the physical interaction between the archaeon Sulfolobus solfataricus Y-family DNA polymerase (SsoPolY) and three eukaryote-like Orc1/Cdc6 proteins (SsoCdc6-1, SsoCdc6-2, and SsoCdc6-3). The effect of SsoCdc6-2 was the strongest, and the three SsoCdc6 proteins were shown to have very different effects on the function of SsoPolY. SsoCdc6-2 inhibited both the DNA-binding activity and DNA polymerization activity of SsoPolY on the DNA substrates containing mismatched bases, while it formed a large complex with SsoPolY and stimulated DNA-binding activity on paired primer-template DNA substrates. SsoCdc6-2 and S. solfataricus PCNA (SsoPCNA) showed a cooperative effect on polymerization by SsoPolY on paired DNA templates, but SsoCdc6 reduced the stimulating effect of SsoPCNA on this polymerization on mismatched DNA substrates. Therefore, we uncovered a DNA substrate-dependent SsoCdc6/SsoPolY interaction mechanism. This is the first evidence for a physical and functional linkage between archaeal eukaryote-like Orc1/Cdc6 proteins and Y-family DNA polymerase.