Abstract

The ROK1 gene encodes a putative ATP-dependent RNA helicase which is essential for mitotic cell growth. ROK1 has been thought to affect microtubule and spindle pole body (SPB) functions in Saccharomyces cerevisiae. To investigate the intracellular functions of ROK1, we varied the Rok1 protein dosage in a cell and analyzed its phenotypic effects. Overexpression of the ROK1 gene by using a strong GAL1 promoter was lethal, leading cells to arrest at the unbudded stage. This arrest phenotype is very similar to that of the rok1 null mutation. Indirect immunofluorescence revealed that the majority of arrested cells contained a single SPB. Normas development of microtubules between the duplicated SPSs was rarely observed. Multinuclear cells with abnormal microtubule array were detected in small fraction. Taken together with the phenotype of the rlk1 null mutation, these results imply that ROK1 is required for cell cycle progression at the G1/S stage.

• Keywords: Saccharomyces cerevisiae; RNA helicase; Rok1p; cell cycle arrest