Thiomethylation of tyrosine transfer ribonucleic acid is associated with initiation of sporulation in Bacillus subtilis: effect of phosphate concentration.

The thiomethylation of Bacillus subtilis tyrosine transfer ribonucleic acid (tRNATyr) (i6A) has been shown to occur during the slowing-down of growth. The extent of this modification in stationary-phase cells grown in defined medium has been determined in parallel with the sporulation frequency. We observed that the presence of phosphate repressed sporulation and also inhibited the thiomethylation of tRNATyr (i6A) of B. subtilis W168. These effects were partially eliminated by decreasing the glucose concentration until it was growth limiting. In the case of strain W23S, in which sporulation is insensitive to glucose repression, sporulation and tRNATyr thiomethylation were not inhibited by nonlimiting concentrations of phosphate. These results suggest that both sporulation and tRNATyr hyper-modification share some common regulatory process.