Evidence for transcriptional and post-transcriptional control of the cellular thymidine kinase gene.
We have studied the cell cycle-regulated expression of the thymidine kinase (TK) gene in mammalian tissue culture cells. TK mRNA and enzyme levels are low in resting, G0-phase cells, but increase dramatically (10- to 20-fold) during the S phase in both serum-stimulated and simian virus 40-infected cells. To determine whether an increase in the rate of TK gene transcription is responsible for this induction, nuclear run-on transcription assays were performed at various times after serum stimulation or simian virus 40 infection of growth-arrested simian CV1 cells. When assays were performed at 12-h intervals, a small (two- to threefold) but reproducible increase in TK transcription was detected during the S phase. When time points were chosen to span the G1-S interface a larger (six- to sevenfold) increase in transcriptional activity was observed in serum-stimulated cells but not in simian virus 40-infected cells. The large increase in TK mRNA levels and the relatively small increase in transcription rates in growth-stimulated cells suggest that TK gene expression is controlled at both a transcriptional and post-transcriptional level during the mammalian cell cycle. To identify the DNA sequences required for cell cycle-regulated expression, several TK cDNA clones were transfected into Rat-3 TK- cells, and their expression was examined in resting and serum-stimulated cultures. These experiments indicated that the body of the TK cDNA is sufficient to insure cell cycle-regulated expression regardless of the promoter or polyadenylation signal used.
D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D002522:Chlorocebus aethiops; D004247:DNA / Q000235:genetics; D005786:Gene Expression Regulation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013937:Thymidine Kinase / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
D012333:RNA, Messenger; D004247:DNA; D013937:Thymidine Kinase