description
In S. cerevisiae, two ORC subunits, Orc1 and Orc5, both bind ATP, and Orc1 in addition has ATPase activity. Both ATP binding and ATP hydrolysis appear to be essential functions in vivo. ATP binding by Orc1 is unaffected by the association of ORC with origin DNA (ARS) sequences, but ATP hydrolysis is ARS-dependent, being suppressed by associated double-stranded DNA and stimulated by associated single-stranded DNA. These data are consistent with the hypothesis that ORC functions as an ATPase switch, hydrolyzing bound ATP and changing state as DNA unwinds at the origin immediately before replication. It is attractive to speculate that ORC likewise functions as a switch as human pre-replicative complexes are activated, but human Orc proteins are not well enough characterized to allow the model to be critically tested. mRNAs encoding human orthologs of all six Orc proteins have been cloned, and ATP-binding amino acid sequence motifs have been identified in Orc1, Orc4, and Orc5. Interactions among proteins expressed from the cloned genes have been characterized, but the ATP-binding and hydrolyzing properties of these proteins and complexes of them have not been determined

external resources
NCBI:1269773
REACTOME:R-HSA-68962
PUBMED:10402192
PUBMED:11779870
PUBMED:10801458
PUBMED:12169736
PUBMED:11323433
PUBMED:9038340
PUBMED:9765232
PUBMED:9829972
PUBMED:10970868
PUBMED:9353276
PUBMED:7502077
PUBMED:11459976
PUBMED:11395502

genes
CDC6 , CDK2 , MCM2 , MCM3 , MCM4 , MCM5 , MCM6 , MCM7 , ORC1 , ORC2 , ORC4 , ORC5 , POLA1 , POLE , POLE2 , PRIM1 , RPA1 , RPA2 , RPA3 , CDC7 , CDC45 , DBF4 , ORC6 , ORC3 , POLA2 , RPA4 , POLE3 , MCM10 , POLE4 , CDT1 , MCM8 ,