Chromatin association of replication protein A

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Replication protein A (RPA) is the primary eukaryotic single-stranded DNA-binding protein.
• Understanding RPA's distribution is crucial for comprehending DNA replication and repair.

Purpose of the Study:

• To investigate the distribution and chromatin association of RPA in proliferating HeLa cells during G1 and S phases.
• To determine RPA's binding status in relation to single-stranded versus double-stranded DNA within the nucleus.

Main Methods:

• Cell synchronization using double thymidine block.
• Fractionation of cellular components to isolate chromatin and nucleosol.
• Enuclease digestion (single strand-specific, DNase I, micrococcal nuclease) to assess RPA release.
• Sucrose gradient centrifugation to analyze released RPA and DNA fragments.

Main Results:

• Only one-third of detectable RPA was bound to DNA in chromatin; the remainder was free in the nucleosol.
• RPA-chromatin association was resistant to single strand-specific endonucleases but sensitive to DNase I and micrococcal nuclease.
• Released RPA did not pellet with mono- or oligonucleosomal fragments, suggesting association with nuclease-accessible chromatin regions.

Conclusions:

• The majority of detectable RPA in HeLa cells (G1 and S phase) is associated with double-stranded DNA regions in chromatin.
• RPA's association may be with more open chromatin structures rather than exclusively with single-stranded DNA intermediates.
• Findings challenge the prevailing view of RPA's primary role as a single-stranded DNA binder in chromatin.