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Mol Cell Biol, April 1998, p. 2055-2066, Vol. 18, No. 4
Banting and Best Department of Medical
Research and Department of Molecular and Medical Genetics,
University of Toronto, Toronto, Ontario, Canada M5G 1L6
Received 8 September 1997/Returned for modification 16 October
1997/Accepted 20 January 1998
A genetic screen was devised to identify Saccharomyces
cerevisiae splicing factors that are important for the function
of the 5' end of U2 snRNA. Six slt (stands for synthetic
lethality with U2) mutants were isolated on the basis of synthetic
lethality with a U2 snRNA mutation that perturbs the U2-U6 snRNA helix
II interaction. SLT11 encodes a new splicing factor and
SLT22 encodes a new RNA-dependent ATPase RNA helicase (D. Xu, S. Nouraini, D. Field, S. J. Tang, and J. D. Friesen,
Nature 381:709-713, 1996). The remaining four slt
mutations are new alleles of previously identified splicing genes:
slt15, previously identified as prp17 (slt15/prp17-100), slt16/smd3-1,
slt17/slu7-100, and slt21/prp8-21. slt11-1 and
slt22-1 are synthetically lethal with mutations in the 3'
end of U6 snRNA, a region that affects U2-U6 snRNA helix II; however,
slt17/slu7-100 and slt21/prp8-21 are not. This
difference suggests that the latter two factors are unlikely to be
involved in interactions with U2-U6 snRNA helix II but rather are
specific to interactions with U2 snRNA. Pairwise synthetic lethality
was observed among slt11-1 (which affects the first step of
splicing) and several second-step factors, including
slt15/prp17-100, slt17/slu7-100, and
prp16-1. Mutations in loop 1 of U5 snRNA, a region that is implicated in the alignment of the two exons, are synthetically lethal
with slu4/prp17-2 and slu7-1 (D. Frank, B. Patterson, and C. Guthrie, Mol. Cell. Biol. 12:5179-5205, 1992), as
well as with slt11-1, slt15/prp17-100,
slt17/slu7-100, and slt21/prp8-21. These same
U5 snRNA mutations also interact genetically with certain U2 snRNA
mutations that lie in the helix I and helix II regions of the U2-U6
snRNA structure. Our results suggest interactions among U2 snRNA, U5
snRNA, and Slt protein factors that may be responsible for coupling and
coordination of the two reactions of pre-mRNA splicing.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Synthetic Lethality of Yeast slt Mutations with U2
Small Nuclear RNA Mutations Suggests Functional Interactions
between U2 and U5 snRNPs That Are Important for Both Steps of
Pre-mRNA Splicing
*
Corresponding author. Mailing address: Banting and Best
Department of Medical Research, University of Toronto, 112 College St.,
Toronto, Ontario, Canada M5G 1L6. Phone: (416) 946-3016. Fax: (416)
978-8528. E-mail: james.friesen{at}utoronto.ca.
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