Fig. 5. Comparison of S. cerevisiae and S. pombe cell cycles. Modified from A. M. Carr and M. F. Hoekstra (1995) The cellular responses to DNA damage. Trends Cell Biol. 5, 32-40. Note that S. cerevisiae duplicates its spindle pole body in late G1, and some spindle elongation occurs during S. Thus M phase in S. cerevisiae overlaps with G1 and S, and there is no clearly defined G2. S. pombe duplicates its spindle pole body immediately before nuclear division, as do most eukaryotes. However, S. pombe is unusual in that,in rapidly dividing cells, cytokinesis does not occur until S phase (which is brief). Thus the smallest S. pombe cells in rapidly growing cultures are in early G2 phase. Most S. pombe cell growth takes place during G2, which occupies the major portion of the S. pombe cell cycle.