Human BIN3 complements the F-actin localization defects caused by loss of Hob3p, the fission yeast homolog of Rvs161p

The BAR adaptor proteins encoded by the RVS167 and RVS161 genes from Saccha romyces cerevisiae form a complex that regulates actin, endocytosis, and vi ability following starvation or osmotic stress. In this study, we identifie d a human homolog of RVS161, termed BIN3 ((b) under bar ridging (i) under b ar ntegrator-3), and a Schizosaccharomyces pombe homolog of RVS161, termed hob3+ (homolog of (B) under bar in3), In human tissues, the BIN3 gene was e xpressed ubiquitously except for brain, S. pombe cells lacking Hob3p were o ften multinucleate and characterized by increased amounts of calcofluor-sta ined material and mislocalized F-actin. For example, while wild-type cells localized F-actin to cell ends during interphase, hob3 Delta mutants had F- actin patches distributed randomly around the cell. In addition, medial F-a ctin rings were rarely found in hob3 Delta mutants. Notably, in contrast to S. cerevisiae rvs161 Delta mutants, hob3 Delta mutants showed no measurabl e defects in endocytosis or response to osmotic stress, yet hob3+ complemen ted the osmosensitivity of a rus161 Delta mutant. BIN3 failed to rescue the osmosensitivity of rvs161 Delta, but the actin localization defects of hob 3 Delta mutants were completely rescued by BIN3 and partially rescued by RV S161, These findings suggest that hob3+ and BIN3 regulate F-actin localizat ion, like RVS161, but that other roles for this gene have diverged somewhat during evolution.