The fifth essential DNA polymerase φ in Saccharomyces cerevisiae is localized to the nucleolus and plays an important role in synthesis of rRNA

doi:10.1073/pnas.142277999

The fifth essential DNA polymerase φ in Saccharomyces cerevisiae is localized to the nucleolus and plays an important role in synthesis of rRNA

Department of Biochemistry and Molecular Biology, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamada-oka, Suita, Osaka 565-0871, Japan

Communicated by Nicholas R. Cozzarelli, University of California, Berkeley, CA (received for review March 20, 2002)

Abstract

We report that POL5 encodes the fifth essential DNA polymerase in Saccharomyces cerevisiae. Pol5p was identified and purified from yeast cell extracts and is an aphidicolin-sensitive DNA polymerase that is stimulated by yeast proliferating cell nuclear antigen (PCNA). Thus, we named Pol5p DNA polymerase φ. Temperature-sensitive pol5-1∼–3 mutants did not arrest at G₂/M at the restrictive temperature. Furthermore, the polymerase active-site mutant POL5dn gene complements the lethality of Δpol5. These results suggest that the polymerase activity of Pol5p is not required for the in vivo function of Pol5p. rRNA synthesis was severely inhibited at the restrictive temperature in the temperature-sensitive pol5-3 mutant cells, suggesting that an essential function of Pol5p is rRNA synthesis. Pol5p is localized exclusively to the nucleolus and binds near or at the enhancer region of rRNA-encoding DNA repeating units.

Footnotes

↵ * On leave from Radioisotope Research Center, Osaka University, Suita, Osaka 565-0871, Japan.
↵ † K.S. and Y.K. contributed equally to this work.
↵ ‡ Present address: Nippon Medical School, Kawasaki, Kanagawa 211-8533, Japan.
↵ § To whom reprint requests should be addressed. E-mail: asugino{at}biken.osaka-u.ac.jp.
Data deposition: The sequence reported in this paper has been deposited in the DNA Data Bank of Japan (DDBJ) database (accession no. AB012696).
Abbreviations:

Pol,

DNA polymerase;

rDNA,

rRNA-encoding DNA;

GST,

glutathione S-transferase;

PCNA,

proliferating cell nuclear antigen