Two independent DNA sequences, of 5.6 and 2.4 kb in size, were isolated from Schizosaccharomyces pombe gene libraries on the basis of their ability to rescue the temperature-conditional lethality conferred by a cdc22 mutation. Integration of these sequences into the S.pombe genome by homologous recombination, followed by genetic mapping, demonstrated that the site of integration of the 5.6 kb fragment is tightly linked to the cdc22 locus, while that of the 2.4 kb fragment is unlinked. This shows that the 5.6 kb fragment carries the authentic cdc22 gene while the 2.4 kb fragment carries and extragenic suppressor sequence. The cdc22 transcript was identified by Northern blot analysis and shown to be 3.3 kb in size. The level of the transcript during the cell cycle was investigated in synchronous cultures prepared by elutriation. The cdc22 transcript is cell cycle regulated, reaching a maximum level during late G1/S phase, at least 12-fold higher than the minimum level observed in mid G2.