M. Kagami et al., SRO7P, A SACCHAROMYCES-CEREVISIAE COUNTERPART OF THE TUMOR-SUPPRESSORL(2)GL PROTEIN, IS RELATED TO MYOSINS IN FUNCTION, Genetics, 149(4), 1998, pp. 1717-1727
Yeast SRO7 was identified as a multicopy suppressor of a defect in Rho
3p, a small GTPase that maintains cell polarity. Sro7p and Sro77p, a h
omologue of Sro7p, possess domains homologous to the protein that are
encoded by the Drosophila tumor suppressor gene lethal (2) giant larva
e [l(2)gl]. sro7 Delta sro77 Delta 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 sro
7 Delta sro77 Delta defect. Similar to the l(2)gl protein, Sro7p forme
d a complex with Myolp, a type II myosin. These results indicate that
Sro7p and Sro77p are the yeast counterparts of the I(2)gl protein. Our
genetic analysis revealed that deletion of SRO7 and SXO77 showed reci
procal suppression with deletion of MYO1 (i.e., the sro7 Delta sro77 D
elta defect was suppressed by myo1 Delta and vice versa). In addition,
SRO7 showed genetic interactions with MYO2, encoding an essential typ
e V myosin: Overexpression of SRO7 suppressed a defect in MYO2 and, co
nversely, overexpression of MYO2 suppressed the cold-sensitive phenoty
pe of sro7 Delta sro77 Delta mutants. These results indicate that Sro7
function is closely related to both Myo1p and Myo2p. We propose a mod
el in which Sro7 function is involved in the targeting of the myosin p
roteins to their intrinsic pathways.