MYO1, a novel, unconventional myosin gene affects endocytosis and macronuclear elongation in Tetrahymena thermophila

Targeted gene disruption was used to investigate the function of MYO1, an u nconventional myosin gene in Tetrahymena thermophila. Phenotypic analysis o f a transformed strain that lacked a functional MYO1 gene was conducted at both 20 degreesC and 35 degreesC. At either temperature the Delta MYO1 stra in had a smaller cytoplasm/nucleus ratio than wild type. At 20 degreesC, De lta MYO1 populations had a longer doubling time than wild type, lower satur ation density, and a reduced rate of food vacuole formation. However, at 35 degreesC, these characteristics were comparable to wild type. Although mic ronuclear division and cytokinesis appeared normal in Delta MYO1 cells, fai lure of the macronucleus to elongate properly resulted in unequal segregati on of macronuclear DNA in cells maintained at either 20 degreesC or 35 degr eesC.