Abstract
Genetic tests with the yeast cell-cycle mutantcdc21 isolated by Hartwell indicate that the CDC21 gene in yeast is the same as the TMP1 gene, whose mutant alleles confer an auxotrophic requirement for thymidine-5′-monophosphate (dTMP). Yeast strains carryingcdc21 can grow at 37° in the presence of dTMP provided that they are permeable to this compound. The gene is shown to be linked toade2 on Chr. XV, and a case of intragenic complementation betweencdc21 and anothertmp1 allele is reported.