Deletion of the sep1(+) forkhead transcription factor homologue is not lethal but causes hyphal growth in Schizosaccharomyces pombe

sep1(+), the Schizosaccharomyces pombe homologue of the forkhead/HNF-3 tran scription factors, plays a role in the cell separation at the end of mitosi s. Its inactivation by interruption of the coding region is not lethal but renders the sister cells unable to separate and causes hyphal growth. The p ersistence of unsplit septa indirectly interferes with the establishment of new cell polarity by preventing cell growth at cell tips. Temporal changes in the transcription of sep1(+) correlate with the cell cycle progression showing maximal expression at the peak of cell plate index in synchronized cultures. The constitutive overexpression of sep1(+) has no discernible eff ect on the morphology and physiology of the cells. (C) 1999 Academic Press.