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Mol. Cell. Biol., 03 1995, 1333-1342, Vol 15, No. 3
V Jung, L Chen, SL Hofmann, M Wigler and S Powers
We have identified a gene, SHR5, in a screen for extragenic suppressors of
the hyperactive RAS2Val-19 mutation in the budding yeast Saccharomyces
cerevisiae. SHR5 was cloned, sequenced, and found to encode a 23-kDa
protein not significantly homologous to other proteins in the current data
bases. Genetic evidence arguing that Shr5 operates at the level of Ras is
presented. We tested whether SHR5, like previously isolated suppressors of
hyperactivated RAS2, acts by affecting the membrane attachment and/or
posttranslational modification of Ras proteins. We found that less Ras
protein is attached to the membrane in shr5 mutants than in wild-type cells
and that the Ras proteins are markedly underpalmitoylated, suggesting that
Shr5 is involved in palmitoylation of Ras proteins. However, shr5null
mutants exhibit normal palmitoyltransferase activity measured in vitro.
Further, shr5null mutations attenuate Ras function in cells containing
mutant Ras2 proteins that are not palmitoylated or farnesylated. We
conclude that SHR5 encodes a protein that participates in the membrane
localization of Ras but also interacts in vivo with completely unprocessed
and cytosolic Ras proteins.
Copyright © 1995, American Society for Microbiology
Mutations in the SHR5 gene of Saccharomyces cerevisiae suppress Ras function and block membrane attachment and palmitoylation of Ras proteins
Cold Spring Harbor Laboratory, New York 11724.
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