Influence of Origin Recognition Complex Proteins on the Copy Numbers of Three Chromosomes in Haloferax volcanii

The core origins of archaea are comprised of a repeat region and an adjacent gene for an origin recognition complex (ORC) protein, which is homologous to eukaryotic ORC proteins.Haloferax volcanii is exceptional because it contains six replication origins on three chromosomes and an additional 10orc genes that are not adjacent to an origin. This unique ORC protein repertoire was used to unravel the importance of core originorc genes and of origin-remoteorc genes. Remarkably, all ORC proteins influenced the copy number of at least one chromosome. Some of them influenced those of all three chromosomes, showing that cross-regulation intrans exists inHfx. volcanii . Furthermore, the evolution of the archaeal ORC protein family was analyzed.