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Molecular and Cellular Biology, November 2005, p. 10183-10189, Vol. 25, No. 22
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.22.10183-10189.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Trf4 and Trf5 Proteins of Saccharomyces cerevisiae Exhibit Poly(A) RNA Polymerase Activity but No DNA Polymerase Activity

Lajos Haracska,1,2 Robert E. Johnson,2 Louise Prakash,2 and Satya Prakash2*

Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, Szeged, Hungary,1 Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston, Texas2

Received 8 August 2005/ Returned for modification 30 August 2005/ Accepted 31 August 2005

The Saccharomyces cerevisiae Trf4 and Trf5 proteins are members of a distinct family of eukaryotic DNA polymerase ß-like nucleotidyltransferases, and a template-dependent DNA polymerase activity has been reported for Trf4. To define the nucleotidyltransferase activities associated with Trf4 and Tr5, we purified these proteins from yeast cells and show that whereas both proteins exhibit a robust poly(A) polymerase activity, neither of them shows any evidence of a DNA polymerase activity. The poly(A) polymerase activity, as determined for Trf4, is strictly Mn2+ dependent and highly ATP specific, incorporating AMP onto the free 3'-hydroxyl end of an RNA primer. Unlike the related poly(A) polymerases from other eukaryotes, which are located in the cytoplasm and regulate the stability and translation efficiency of specific mRNAs, the Trf4 and Trf5 proteins are nuclear, and a multiprotein complex associated with Trf4 has been recently shown to polyadenylate a variety of misfolded or inappropriately expressed RNAs which activate their degradation by the exosome. To account for the effects of Trf4/Trf5 proteins on the various aspects of DNA metabolism, including chromosome condensation, DNA replication, and sister chromatid cohesion, we suggest an additional and essential role for the Trf4 and Trf5 protein complexes in generating functional mRNA poly(A) tails in the nucleus.

* Corresponding author. Mailing address: Sealy Center for Molecular Science, University of Texas Medical Branch at Galveston, Galveston, TX 77555-1061. Phone: (409) 747-8602. Fax: (409) 747-8608. E-mail: s.prakash{at}utmb.edu.

Molecular and Cellular Biology, November 2005, p. 10183-10189, Vol. 25, No. 22
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.22.10183-10189.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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