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Mol. Cell. Biol., 01 1998, 353-360, Vol 18, No. 1
MR McLean and BC Rymond
The U1 snRNP functions to nucleate spliceosome assembly on newly
transcribed pre-mRNA. Saccharomyces cerevisiae is unusual among eukaryotes
in the greatly extended length of its U1 snRNA and the apparent increased
polypeptide complexity of the corresponding U1 snRNP. In this paper, we
report the identification of a novel U1 snRNP protein, Prp42p, with
unexpected properties. Prp42p was identified by its surprising structural
similarity to the essential U1 snRNP protein, Prp39p. Both Prp39p and
Prp42p possess multiple copies of a variant tetratricopeptide repeat, an
element implicated in a wide range of protein assembly events. Yeast
strains depleted of Prp42p by transcriptional repression of a GAL1::PRP42
fusion gene arrest for splicing prior to pre-mRNA 5' splice site cleavage.
Prp42p was not observed in a recent biochemical analysis of purified U1
snRNPs from S. cerevisiae (28). Nevertheless, antibodies directed against
an epitope- tagged version of Prp42p specifically precipitate U1 snRNA from
yeast extracts. Furthermore, Prp42p is required for U1 snRNP biogenesis,
because yeast strains depleted of Prp42p formed incomplete U1 snRNPs that
failed to produce stable complexes with pre-mRNA in vitro. The evidence
shows that Prp39p and Prp42p are both required to configure the atypical
yeast U1 snRNP into a structure compatible with its evolutionarily
conserved role in pre-mRNA splicing.
Copyright © 1998, American Society for Microbiology
Yeast pre-mRNA splicing requires a pair of U1 snRNP-associated tetratricopeptide repeat proteins
T. H. Morgan School of Biological Sciences, University of Kentucky, Lexington 40506-0225, USA.
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