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Molecular and Cellular Biology, December 1998, p. 7383-7396, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Pbp1p, a Factor Interacting with Saccharomyces cerevisiae Poly(A)-Binding Protein, Regulates Polyadenylation

David A. Mangus, Nadia Amrani, and Allan Jacobson*

Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655-0122

Received 18 June 1998/Returned for modification 3 August 1998/Accepted 20 August 1998

The poly(A) tail of an mRNA is believed to influence the initiation of translation, and the rate at which the poly(A) tail is removed is thought to determine how fast an mRNA is degraded. One key factor associated with this 3'-end structure is the poly(A)-binding protein (Pab1p) encoded by the PAB1 gene in Saccharomyces cerevisiae. In an effort to learn more about the functional role of this protein, we used a two-hybrid screen to determine the factor(s) with which it interacts. We identified five genes encoding factors that specifically interact with the carboxy terminus of Pab1p. Of a total of 44 specific clones identified, PBP1 (for Pab1p-binding protein) was isolated 38 times. Of the putative interacting genes examined, PBP1 promoted the highest level of resistance to 3-aminotriazole (>100 mM) in constructs in which HIS3 was used as a reporter. We determined that a fraction of Pbp1p cosediments with polysomes in sucrose gradients and that its distribution is very similar to that of Pab1p. Disruption of PBP1 showed that it is not essential for viability but can suppress the lethality associated with a PAB1 deletion. The suppression of pab1Delta by pbp1Delta appears to be different from that mediated by other pab1 suppressors, since disruption of PBP1 does not alter translation rates, affect accumulation of ribosomal subunits, change mRNA poly(A) tail lengths, or result in a defect in mRNA decay. Rather, Pbp1p appears to function in the nucleus to promote proper polyadenylation. In the absence of Pbp1p, 3' termini of pre-mRNAs are properly cleaved but lack full-length poly(A) tails. These effects suggest that Pbp1p may act to repress the ability of Pab1p to negatively regulate polyadenylation.

* Corresponding author. Mailing address: Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, 55 Lake Ave. North, Worcester, MA 01655-0122. Phone: (508) 856-2442. Fax: (508) 856-5920. E-mail: ajacob{at}ummed.edu.

Molecular and Cellular Biology, December 1998, p. 7383-7396, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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