An in vivo analysis of the localisation and interactions of human p66 DNA polymerase delta subunit.
BACKGROUND
DNA polymerase delta is essential for eukaryotic DNA replication and also plays a role in DNA repair. The processivity of this polymerase complex is dependent upon its interaction with the sliding clamp PCNA and the polymerase-PCNA interaction is largely mediated through the p66 polymerase subunit. We have analysed the interactions of the human p66 DNA polymerase delta subunit with PCNA and with components of the DNA polymerase delta complex in vivo.


RESULTS
Using the two-hybrid system, we have mapped the interaction domains for binding to the p50 polymerase delta subunit and with PCNA to the N-terminus and the C-terminus of p66, respectively. Co-immunoprecipitation experiments confirm that these interaction domains are functional in vivo. Expression of EGFP-p66 shows that it is a nuclear protein which co-localises with PCNA throughout the cell cycle. p66 is localised to sites of DNA replication during S phase and to repair foci following DNA damage. We have identified a functional nuclear localisation sequence and shown that localisation to replication foci is not dependent upon active nuclear import. Sub-domains of p66 act as dominant negative suppressors of colony formation, suggesting that p66 forms an essential structural link between the p50 subunit and PCNA. Analysis of the C-terminal PCNA binding motif shows that deletion of the QVSITGFF core motif results in a reduced affinity for PCNA, while deletion of a further 20 amino acids completely abolishes the interaction. A reduced affinity for PCNA correlates with reduced targeting to replication foci. We have confirmed the p66-PCNA interaction in vivo using fluorescence resonance energy transfer (FRET) techniques.


CONCLUSIONS
We have defined the regions of p66 required for its interaction with PCNA and the p50 polymerase subunit. We demonstrate a functional link between PCNA interaction and localisation to replication foci and show that there is a direct interaction between p66 and PCNA in living cells during DNA replication. The dominant negative effect upon growth resulting from expression of p66 sub-domains confirms that the p66-PCNA interaction is essential in vivo.
Department of Surgery and Molecular Oncology, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK. jrgpohler@hotmail.com
J Richard G
JR
Pohler
Marit
M
Otterlei
Emma
E
Warbrick
D000595:Amino Acid Sequence; D001665:Binding Sites; D002453:Cell Cycle; D045744:Cell Line, Tumor; D004258:DNA Polymerase III / Q000032:analysis / Q000378:metabolism*; D004261:DNA Replication; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism*; D025941:Protein Interaction Mapping; D014162:Transfection
D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D018809:Proliferating Cell Nuclear Antigen; C435720:POLD3 protein, human; D004258:DNA Polymerase III