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MOLECULAR AND CELLULAR BIOLOGY, Mar. 1996, p. 818828 Vol. 16, No. 3 0270-7306/96/$04.00 0

Summary: MOLECULAR AND CELLULAR BIOLOGY, Mar. 1996, p. 818828 Vol. 16, No. 3
0270-7306/96/$04.00 0
Copyright 1996, American Society for Microbiology
Invariant U2 RNA Sequences Bordering the Branchpoint Recognition
Region Are Essential for Interaction with Yeast
SF3a and SF3b Subunits
Biology Department, Sinsheimer Laboratories, University of California,
Santa Cruz, Santa Cruz, California 95064
Received 5 September 1995/Returned for modification 30 October 1995/Accepted 29 November 1995
U2 small nuclear RNA (snRNA) contains a sequence (GUAGUA) that pairs with the intron branchpoint
during splicing. This sequence is contained within a longer invariant sequence of unknown secondary structure
and function that extends between U2 stem I and stem IIa. A part of this region has been proposed to pair with
U6 in a structure called helix III. We made mutations to test the function of these nucleotides in yeast U2
snRNA. Most single base changes cause no obvious growth defects; however, several single and double muta-
tions are lethal or conditional lethal and cause a block before the first step of splicing. We used U6 compen-
satory mutations to assess the contribution of helix III and found that if it forms, helix III is dispensable for
splicing in Saccharomyces cerevisiae. On the other hand, mutations in known protein components of the splicing
apparatus suppress or enhance the phenotypes of mutations within the invariant sequence that connect the
branchpoint recognition sequence to stem IIa. Lethal mutations in the region are suppressed by Cus1-54p, a


Source: Ares Jr., Manny - Department of Molecular, Cell, and Developmental Biology, University of California at Santa Cruz


Collections: Biology and Medicine