Lysine tRNA modification has been studied in mammalian ts-694 cells with respect to cell cycle progression in temperature downshift and upshift experiments. The modification of tRNAlys measured in temperature downshift experiments showed that tRNA4lys levels start to increase 6 h following the temperature shift, approximately 10-12 h prior to the cells entry into S phase. Ts-694 cells showed a gradual decrease in the level of tRNA4lys and the rates of DNA synthesis following a temperature upshift. The cells became growth arrested following incubation for 36-45 h at the rt. Cell cycle mapping of the temperature restriction point suggests a G1 block prior to the serum deprivation restriction point. Depletion of cellular tRNA4lys by serum deprivation followed by simultaneously shifting cells to the rt and feeding medium containing 10% serum showed that cells with low tRNA4lys levels and no mechanism for the synthesis of tRNA4lys could not enter S phase and synthesize DNA. Blocking of ts-694 at the G1 S boundary with aphidicolin indicates that cells that have passed through G1 are capable of entering S phase and synthesizing DNA independent of the incubation temperature. These results indicate that tRNA4lys is not needed during S phase for DNA replication but suggests that tRNA4lys is required for cells to progress through G1.
ASJC Scopus subject areas
- Cell Biology