Cdc6p modulates the structure and DNA binding activity of the origin recognition complex in vitro

An interaction between the origin recognition complex (ORC) and Cdc6p is th e first and a key step in the initiation of chromosomal DNA replication. We describe the assembly of an origin-dependent complex containing ORC and Cd c6p from Saccharomyces cerevisiae. Cdc6p increases the DNA binding specific ity of ORC by inhibiting non-specific DNA binding of ORC. Cdc6p induces a c oncomitant change in the conformation of ORC and mutations in the Cdc6p Wal ker A and Walker B motifs, or ATP-gamma-S inhibited these activities of Cdc 6p. These data suggest that Cdc6p modifies ORC function at DNA replication origins. On the basis of these results in yeast, we propose that Cdc6p may be an essential determinant of origin specificity in metazoan species.