Journal Article

Nucleolar Protein B23.1 Binds to Retinoblastoma Protein and Synergistically Stimulates DNA Polymerase α Activity

Masaharu Takemura, Keiji Sato, Masahiro Nishio, Tetsu Akiyama, Hayato Umekawa and Shorten Yoshida

in The Journal of Biochemistry

Published on behalf of The Japanese Biochemical Society

Volume 125, issue 5, pages 904-909
Published in print May 1999 | ISSN: 0021-924X
Published online May 1999 | e-ISSN: 1756-2651 | DOI: https://dx.doi.org/10.1093/oxfordjournals.jbchem.a022367
Nucleolar Protein B23.1 Binds to Retinoblastoma Protein and Synergistically Stimulates DNA Polymerase α Activity

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Phosphorylated retinoblastoma protein and nucleolar protein B23 are putative stimulatory factors for DNA polymerase α. We showed that these two factors interacted with each other and stimulated the activity of DNA polymerase α synergistically. B23 exists in two iso-forms designated as B23.1 and B23.2. While B23.1 bound to a retinoblastoma protein-conjugated column, B23.2 did not. These results indicate that B23.1 can directly bind to retinoblastoma protein. It was also shown that B23 was co-immunoprecipitated with both retinoblastoma protein and DNA polymerase α from a HeLa cell extract by monoclonal antibodies raised against these components. These results suggest that these three proteins exist as a complex in cells, at least in part. The simultaneous addition of both B23.1 and retinoblastoma protein caused stimulation of DNA polymerase α activity that is much higher than the sum of the stimulation by retinoblastoma protein and B23.1 alone. The maximal stimulation was attained at the molar ratio of DNA polymerase α/retinoblastoma protei/B23.1 = 1:1:12. Since B23 exists as a hexamer in solution, it may act as a stimulator of DNA polymerase α in a form of double-hexamer, in concert with the phosphorylated retinoblastoma protein

Keywords: B23; DNA polymerase α; DNA replication; oligomerization; retinoblastoma protein.

Journal Article.  0 words. 

Subjects: Biochemistry

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