Independent regulation of thymidine kinase mRNA and enzyme levels in serum-stimulated cells.
We have studied the regulation of thymidine kinase mRNA and protein/enzyme expression in quiescent and serum-stimulated rat cells transfected with a human TK cDNA clone expressed from a number of promoters. Our results indicate that while the pattern of mRNA expression is a function of the promoter used, the pattern of protein/enzyme expression is not. When the gene is expressed from the homologous human TK promoter both mRNA and enzyme levels remain low throughout G1 and increase as the cells enter S phase. When it is expressed from the heterologous SV40 early promoter, mRNA levels are high throughout G1, but enzyme and protein levels remain low until 8-10 h following serum stimulation. Thus, protein levels appear to be uncoupled from mRNA levels in this system, suggesting the presence of translational and/or posttranslational regulation. An analysis of mutant cDNA clones indicates that this regulation is not dependent upon sequences at the 5' or 3' end of the cDNA, including the entire 5'-untranslated region, the authentic AUG and the first 48 nucleotides of the coding region.
Ito
M
M
Department of Microbiology, Michigan State University, East Lansing 48824-1101.
Conrad
S E
SE
D000818:Animals; D001769:Blood; D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D003470:Culture Media; D004247:DNA / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007700:Kinetics; D011401:Promoter Regions, Genetic; D012313:RNA / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics* / Q000302:isolation & purification; D051381:Rats; D013937:Thymidine Kinase / Q000235:genetics*; D014162:Transfection
D003470:Culture Media; D012333:RNA, Messenger; D012313:RNA; D004247:DNA; D013937:Thymidine Kinase