Site-specific ORC binding, pre-replication complex assembly and DNA synthesis at Schizosaccharomyces pombe replication origins

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• The Origin Recognition Complex (ORC) is crucial for DNA replication initiation.
• Previous research identified the Schizosaccharomyces pombe Orc4 subunit as key for ORC binding to AT-rich sites in replication origins.

Purpose of the Study:

• To investigate the in situ and in vitro binding of Orc4 to the ARS3001 replication origin in Schizosaccharomyces pombe.
• To characterize the functional elements within ARS3001 and their roles in DNA replication initiation.

Main Methods:

• In vitro and in situ binding assays using the ARS3001 replication origin.
• Analysis of Orc4 binding patterns to different sites within ARS3001.
• Investigation of protein-DNA interactions during the cell cycle.

Main Results:

• Orc4 binds strongly to the Delta3 site and weakly to the Delta6 site of ARS3001, with no binding to other sequences.
• In G1 phase, the Orc4 footprint at Delta3 extends to the Delta2 site when Cdc18 and Mcm proteins are present.
• A novel origin element, Delta9, binds an unidentified protein throughout the cell cycle but does not bind ORC or function as a centromere.

Conclusions:

• ARS3001 functions as a single primary ORC binding site that initiates pre-replication complex assembly and DNA synthesis.
• ARS3001 contains a novel origin element (Delta9) with a cell-cycle independent binding protein.
• Schizosaccharomyces pombe may serve as a model for complex metazoan replication origins.