The RCC1 gene has been isolated from several vertebrates, including human, hamster and Xenopus. Genes similar to RCC1, namely BJ1 and SRM1/PRP20, have been isolated from the insect Drosophila and from the budding yeast Saccharomyces cerevisiae. A mutation of the RCC1 gene in the hamster BHK21 cell line, tsBN2, confers pleiotropic phenotypes, including G1 arrest and premature induction of mitosis in cells synchronized at the G1/S boundary. Similarly, mutations of the SRM1/PRP20 gene are pleiotropic; the srm1 mutant shows G1 arrest and suppression of the mating defect of mutants lacking pheromone receptors, and the prp20 mutant shows an alteration in mRNA metabolism. Here we show that both BJ1 and SRM1/PRP20 complement the temperature sensitive phenotype of the tsBN2 cells. Like RCC1 proteins of vertebrates, the protein products of the Drosophila and yeast RCC1 homologues were located in the nuclei of the mammalian cells. These results suggest that the BJ1 and SRM1/PRP20 genes are functionally equivalent to the vertebrate RCC1 genes, and that the RCC1 gene plays an important role in the regulation of gene expression in the eukaryotic cell cycle.