Nucleic acid metabolism in yeast. I. Inhibition of RNA and DNA synthesis by high concentrations of exogenous deoxythymidine 5'-monophosphate in 5'-dTMP low requiring strains.

The three haploid yeast strains T2tmpl1-3, T2tmp1-1, and T6tmp1-51 auxotrophic for 5'-dTMP differ in their requirement for thymidylate: 72, 16, and 3 mug 5'-dTMP/ml will restore optimal growth, respectively. Thymidylate low requirement in strain T2tmp1-1 and T6tmp1-51 is termed tlrA and tlrC, respectively. When the growth medium is made 5 x 10(-4) M for 5'-dTMP only strain T6tmp1-51 is severely inhibited in RNA and DNA synthesis. This inhibition is reversible after removal of excessive 5'-dTMP. The inhibitory characteristic is in marked contrast to "thymineless death" due to the lack of 5'-dTMP in strain T6tmp1-51 where only DNA synthesis stops while RNA synthesis continues. The inhibitory effect of 5 x 10(-4) M 5'-dTMP is not due to the 5'-dTMP auxotrophy but to the thymidylate low requiring character (tlrC) in strain T6tmp1-51. The arrest of RNA and DNA synthesis by high concentrations of exogenous 5'-dTMP suggests a regulatory role of either the mono- or triphosphate on nucleoside or nucleotide biosynthesis in yeast.