Periodic accumulation of cdc15 mRNA is not necessary for septation in Schizosaccharomyces pombe

Analysis of Schizosaccharomyces pombe mutants that are defective in septum formation and cytokinesis has identified the product of the cdc15 gene as a key element in formation of a division septum. S. pombe cells lacking cdc1 5p function cannot assemble a functional medial ring, and do not make a div ision septum. cdc25 mRNA accumulates periodically during the cell cycle, pe aking after entry into mitosis, and increased expression of the gene in G2- arrested cells can promote F-actin ring formation. Here, we have investigat ed the effects of mutations that block cell division upon the expression of cdc15 in synchronised cell populations, and analysed the expression of cdc 15 when septum formation is induced by ectopic activation of the septation signalling network. We concluded the following: (i) the septation signallin g network genes are not required for periodic accumulation of cdcl5 mRNA; ( ii) induction of septum formation in G2-arrested cells by activation of the septation signalling network does not result in accumulation of cdcl5 mRNA , which is therefore not a prerequisite for septum formation; (iii) failure to turn off septum formation at the end of mitosis results in continued ex pression of cdcl5; and (iv) periodic accumulation of cdc15 mRNA is mediated by a 97 bp region 5' to the mRNA start site. (C) 2000 Academic Press.