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Mol. Cell. Biol., 03 1995, 1689-1697, Vol 15, No. 3
R Russnak, KW Nehrke and T Platt
The Saccharomyces cerevisiae mutant ref2-1 (REF = RNA end formation) was
originally identified by a genetic strategy predicted to detect decreases
in the use of a CYC1 poly(A) site interposed within the intron of an
ACT1-HIS4 fusion reporter gene. Direct RNA analysis now proves this effect
and also demonstrates the trans action of the REF2 gene product on cryptic
poly(A) sites located within the coding region of a plasmid-borne ACT1-lacZ
gene. Despite impaired growth of ref2 strains, possibly because of a
general defect in the efficiency of mRNA 3'-end processing, the
steady-state characteristics of a variety of normal cellular mRNAs remain
unaffected. Sequencing of the complementing gene predicts the Ref2p product
to be a novel, basic protein of 429 amino acids (M(r), 48,000) with a
high-level lysine/serine content and some unusual features. Analysis in
vitro, with a number of defined RNA substrates, confirms that efficient use
of weak poly(A) sites requires Ref2p: endonucleolytic cleavage is carried
out accurately but at significantly lower rates in extracts prepared from
delta ref2 cells. The addition of purified, epitope-tagged Ref2p (Ref2pF)
reestablishes wild-type levels of activity in these extracts, demonstrating
direct involvement of this protein in the cleavage step of 3' mRNA
processing. Together with the RNA-binding characteristics of Ref2pF in
vitro, our results support an important contributing role for the REF2
locus in 3'-end processing. As the first gene genetically identified to
participate in mRNA 3'-end maturation prior to the final polyadenylation
step, REF2 provides an ideal starting point for identifying related genes
in this event.
Copyright © 1995, American Society for Microbiology
REF2 encodes an RNA-binding protein directly involved in yeast mRNA 3'- end formation
Department of Biochemistry, University of Rochester, New York 14642.
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