Sro7p, a Saccharomyces cerevisiae Counterpart of the Tumor Suppressor l(2)gl Protein, Is Related to Myosins in Function

Corresponding author: Yasushi Matsui, Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1, Hongo, Tokyo 113, Japan., matsui{at}biol.s.u-tokyo.ac.jp (E-mail).

Communicating editor: F. WINSTON

Yeast SRO7 was identified as a multicopy suppressor of a defect in Rho3p, a small GTPase that maintains cell polarity. Sro7p and Sro77p, a homologue of Sro7p, possess domains homologous to the protein that are encoded by the Drosophila tumor suppressor gene lethal (2) giant larvae [l(2)gl]. sro7 sro77 mutants showed a partial defect of organization of the polarized actin cytoskeleton and a cold-sensitive growth phenotype. A human counterpart of l(2)gl could suppress the sro7 sro77 defect. Similar to the l(2)gl protein, Sro7p formed a complex with Myo1p, a type II myosin. These results indicate that Sro7p and Sro77p are the yeast counterparts of the l(2)gl protein. Our genetic analysis revealed that deletion of SRO7 and SRO77 showed reciprocal suppression with deletion of MYO1 (i.e., the sro7 sro77 defect was suppressed by myo1 and vice versa). In addition, SRO7 showed genetic interactions with MYO2, encoding an essential type V myosin: Overexpression of SRO7 suppressed a defect in MYO2 and, conversely, overexpression of MYO2 suppressed the cold-sensitive phenotype of sro7 sro77 mutants. These results indicate that Sro7 function is closely related to both Myo1p and Myo2p. We propose a model in which Sro7 function is involved in the targeting of the myosin proteins to their intrinsic pathways.

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