Abstract
The six-subunit Origin Recognition Complex (ORC) is believed to be an essential eukaryotic ATPase that binds to origins of replication as a ring-shaped heterohexamer to load MCM2-7 and initiate DNA replication. We have discovered that human cell lines in culture proliferate with intact chromosomal origins of replication after disruption of both alleles of ORC2 or of the ATPase subunit, ORC1. The ORC1 or ORC2-depleted cells replicate with decreased chromatin loading of MCM2-7 and become critically dependent on another ATPase, CDC6, for survival and DNA replication. Thus, either the ORC ring lacking a subunit, even its ATPase subunit, can load enough MCM2-7 in partnership with CDC6 to initiate DNA replication, or cells have an ORC-independent, CDC6-dependent mechanism to load MCM2-7 on origins of replication.
Highlights
The discovery of the six-subunit Origin Recognition Complex (ORC) (Bell and Stillman, 1992) identified the long sought initiator protein that binds to replicator sequences to initiate DNA replication in eukaryotes
The surprising results from this genetic investigation of ORC in human cell lines suggest that two subunits of ORC are dispensable for DNA replication
We believe that no ORC2 protein is synthesized in the ORC2-/- cells, we have to entertain the caveat that up to 1530 ORC2 molecules can escape the limits of detection with our current antibodies
Summary
The discovery of the six-subunit ORC (Bell and Stillman, 1992) identified the long sought initiator protein that binds to replicator sequences to initiate DNA replication in eukaryotes. ORC is an essential six-subunit, ring-shaped ATPase complex that recruits and co-operates with the CDC6 protein to promote the loading of CDT1 and the MCM2-7 subunits of the replicative helicase during the ‘licensing’ of origins of replication (Bleichert et al, 2015; Yeeles et al, 2015; Bell and Stillman, 1992; Blow and Tada, 2000; Masai et al, 2010). It is expected that eukaryotic cells will not be viable, and will not replicate, if any of the ORC subunit genes are deleted. We have deleted both alleles of human ORC2 or of ORC1, to discover that cells can still survive and replicate in the complete absence of either of these two critical subunits of Origin Recognition Complex
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
