Caenorhabditis elegans SUR-5, a Novel but Conserved Protein, Negatively Regulates LET-60 Ras Activity during Vulval Induction

ABSTRACT

The let-60 ras gene acts in a signal transduction pathway to control vulval differentiation in Caenorhabditis elegans. By screening suppressors of a dominant negativelet-60 ras allele, we isolated three loss-of-function mutations in the sur-5 gene which appear to act as negative regulators of let-60 ras during vulval induction.sur-5 mutations do not cause an obvious mutant phenotype of their own, and they appear to specifically suppress only one of the two groups of let-60 ras dominant negative mutations, suggesting that the gene may be involved in a specific aspect of Ras activation. Consistent with its negative function, overexpressing sur-5 from an extragenic array partially suppresses the Multivulva phenotype of an activatedlet-60 ras mutation and causes synergistic phenotypes with a lin-45 raf mutation. We have clonedsur-5 and shown that it encodes a novel protein. We have also identified a potential mammalian SUR-5 homolog that is about 35% identical to the worm protein. SUR-5 also has some sequence similarity to acetyl coenzyme A synthetases and is predicted to contain ATP/GTP and AMP binding sites. Our results suggest thatsur-5 gene function may be conserved through evolution.

ACKNOWLEDGMENTS

We thank A. Coulson, A. Fire, and D. Pilgrim for providing DNA clones, and we thank S. Clark and H. R. Horvitz for providing several let-60 alleles. Some strains were provided by the Caenorhabditis Genetics Center, which is funded by the NIH National Center for Research Resources. We also thank W. Wood, N. Ahn, J. Yochem, M. Sundaram, Y. Wu, N. Singh, C. Malone, D. Seiberth, and rest of the Han laboratory for helpful discussion throughout the course of the study, and we thank W. Wood, C. Bartholomew, W. Hanna-Rose, and I. Antoshechkin for comments on the manuscript.

This research has been supported by grants from NIH (GM47869) and American Cancer Society. T.G. was an NIH predoctoral trainee. M.H. was a Lucille P. Markey Scholar and a Searle Scholar and is an assistant investigator of Howard Hughes Medical Institute.