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.
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 pab1
by pbp1
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.
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