A suppressor of a yeast splicing mutation (prp8-l) encodes a putative ATP-dependent RNA helicase

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Abstract
FIVE small nuclear RNAs (snRNAs) are required for nuclear pre-messenger RNA splicing: Ul, U2, U4, U5 and U61,2. The yeast Ul and U2 snRNAs base-pair to the 5′ splice site and branch-point sequences of introns respectively1. The role of the U5 and U4/U6 small nuclear ribonucleoprotein particles (snRNPs) in splicing is not clear, though a catalytic role for the U6 snRNA has been proposed3. Less is known about yeast splicing factors, but the availability of genetic techniques in Saccharomyces cerevisiae has led to the identification of mutants deficient in nuclear pre-mRNA splicing (prp2-prp27)4,5. Several PRP genes have now been cloned and their protein products characterized. The PRP8 protein is a component of the US snRNP and associates with the U4/U6 snRNAs/snRNP to form a multi-snRNP particle believed to be important for spliceosome assembly6. We have isolated extragenic suppressors of the prp8–l mutation of S. cerevisiae and present here the preliminary characterization of one of these suppressors, spp81. The predicted amino-acid sequence of the SPP81protein shows extensive similarity to a recently identified family of proteins thought to possess ATP–dependent RNA helicase activity. The possible role of this putative helicase in nuclear pre-mRNA splicing is discussed.