CALCIUM-INDEPENDENT CALMODULIN REQUIREMENT FOR ENDOCYTOSIS IN YEAST

We have recently shown that actin and fimbrin are required for the int ernalization step of endocytosis in yeast. Using a yeast strain with a temperature-sensitive allele of CMD1, encoding calmodulin, we demonst rate that this protein is also required for this process. Calmodulin m utants that have lost their high-affinity calcium binding sites are, h owever, able to carry out endocytosis normally. A mutation in Myo2p, a n unconventional myosin that is a possible target of calmodulin, did n ot inhibit endocytosis. The function of calmodulin in endocytosis seem s to be specific among membrane trafficking events, because the calmod ulin mutants are not defective for biogenesis of soluble vacuolar hydr olases nor invertase secretion. Calmodulin does not seem to play a maj or role in the post-internalization steps of the endocytic pathway in yeast.