Specificity and function of archaeal DNA replication initiator proteins

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Eukaryotic and archaeal chromosomes utilize multiple DNA replication origins.
• Eukaryal replication origins are recognized by the Origin Recognition Complex (ORC) and involve MCM(2-7) helicase recruitment via Cdc6 and Cdt1.

Purpose of the Study:

• To investigate the distinct initiation factors specifying replication origins in the archaeon *Sulfolobus islandicus*.
• To elucidate the role of ATP binding and hydrolysis in Orc1-1 initiator function in vivo and in vitro.

Main Methods:

• Comparative analysis of replication origin specification in *Sulfolobus islandicus*.
• In vivo and in vitro assays utilizing the nonessential orc1-1 gene to study Orc1-1 function.
• Biochemical analysis of ATP and DNA binding effects on Orc1-1 structure.

Main Results:

• *Sulfolobus islandicus* replication origins are specified by distinct initiation factors: two by Orc1 and Cdc6 homologs, one by a Cdt1 homolog.
• The ATP-bound form of Orc1-1 is essential for replication initiation.
• ATP hydrolysis by Orc1-1 downregulates origin activity.
• Orc1-1 undergoes structural remodeling upon ATP and DNA binding, rather than altering the DNA template.

Conclusions:

• Replication origin specification in *Sulfolobus islandicus* involves a unique combination of archaeal homologs of eukaryotic initiation factors.
• Orc1-1's ATP binding and hydrolysis cycle regulates DNA replication initiation and termination.
• Orc1-1 functions as a regulatory switch, modulating replication activity through structural changes.