A novel Rad24 checkpoint protein complex closely related to replication factor C

Area of Science:

• Molecular Biology
• Cellular Biology
• Biochemistry

Background:

• Rad24 is a key protein in the DNA damage checkpoint pathway in Saccharomyces cerevisiae.
• Previous studies indicated Rad24's role in DNA repair and replication.
• The precise molecular interactions and complex formation of Rad24 were not fully understood.

Purpose of the Study:

• To investigate the molecular composition of Rad24 within Saccharomyces cerevisiae.
• To identify other proteins that interact with Rad24.
• To elucidate the potential function of the Rad24 complex in DNA damage response.

Main Methods:

• Analysis of whole cell extracts to determine Rad24's molecular weight.
• Purification of the Rad24 complex.
• Mass spectrometry to identify complex components.
• Reciprocal co-immunoprecipitation assays using epitope-tagged RFC proteins.

Main Results:

• Rad24 exists in a protein complex with a significantly higher molecular weight than predicted.
• The purified Rad24 complex contains polypeptides of 40 kDa and 35 kDa.
• Mass spectrometry identified Rfc2 and Rfc3 (subunits of Replication Factor C) within the 40 kDa species.
• Co-immunoprecipitation confirmed interactions between Rad24 and RFC subunits Rfc2, Rfc3, Rfc4, and Rfc5, but not Rfc1.

Conclusions:

• Rad24 forms an RFC-like complex with specific RFC subunits (Rfc2-Rfc5).
• This complex is distinct from the canonical Replication Factor C complex due to the absence of Rfc1.
• The RFC-like Rad24 complex is proposed to function as a structure-specific sensor in the DNA damage checkpoint pathway.