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Takemura, M. et al.

Takemura, Yoshida, Akiyama, Kitagawa, Yamada,

Role of the second-largest subunit of DNA polymerase alpha in the interaction between the catalytic subunit and hyperphosphorylated retinoblastoma protein in late S phase.

DNA polymerase alpha ( pol-alpha) is a heterotetrameric enzyme ( p180- p68- p58- p48 in mouse) that is essential for the initiation of chain elongation during DNA replication. The catalytic ( p180) and p68 subunits of pol-alpha are phosphorylated by Cdk-cyclin complexes, with p68 being hyperphosphorylated by cyclin-dependent kinases in G(2) phase of the cell cycle. The activity of Cdk2-cyclin A increases during late S phase and peaks in G(2) phase. We have now examined the role of p68 in the interaction between the catalytic subunit of pol-alpha and hyperphosphorylated retinoblastoma protein (ppRb) and in the stimulation of the polymerase activity of pol-alpha by ppRb. With the use of recombinant proteins, we found that nonphosphorylated p68 inhibited the stimulation of pol-alpha activity by ppRb, suggesting that p68 might impede the association of ppRb with p180. Phosphorylation of p68 by Cdk2-cyclin A greatly reduced its inhibitory effect. Immunofluorescence analysis also revealed that ppRb localized at sites of DNA replication specifically in late S phase. These results suggest that Cdk-cyclin A can phosphorylate pol-alpha which may result in a conformational change in pol-alpha facilitating its interaction with and activation by ppRb.[1]

References

Role of the second-largest subunit of DNA polymerase alpha in the interaction between the catalytic subunit and hyperphosphorylated retinoblastoma protein in late S phase. Takemura, M., Yoshida, S., Akiyama, T., Kitagawa, M., Yamada, Y. Biochim. Biophys. Acta (2006) [Pubmed]

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