The kinetics of H1 histone kinase activation during the cell cycle of wild-type and wee mutants of the fission yeast Schizosaccharomyces pombe

Abstract

H1 histone kinase activity has been followed in selection-synchronised cultures of fission yeast wild-type and wee1 mutant cells, and in induction-synchronised cells of the mutant cdc2-33. The main conclusions are: (1) in all three cases, the peak of activity is near mitosis. (2) The rise in activity is relatively slow starting in wild type at 0.4 of the cycle before mitosis. It is proposed that the beginning of the rise is the first identified event in the mitotic control. (3) The rise is twice as fast in wee and starts nearer to mitosis. (4) In all cases the beginning of the rise is in G2. (5) The fall in activity is also slow, lasting for 0.25 of the cycle, in wild type. Exit from mitosis happens well before activity has fallen to baseline. (6) In a range of size mutants, activity is roughly proportional to cell size. It is suggested that the kinase may have a cytoplasmic function. (7) Estimates have been made of the timing of mitosis in the mutants. In wee, mitosis is 0.14 of the cycle earlier than in wild type because the cells have a longer septated period at the end of the cycle. (8) A novel method has been developed for eliminating the effects of the partial asynchrony in synchronous cultures, without which the kinetic analysis would have been inaccurate.