Constitutive protection of E2F recognition sequences in the human thymidine kinase promoter during cell cycle progression.
The sequences responsible for S phase-specific induction of the human thymidine kinase (TK) gene have been mapped to a small region that contains putative E2F binding sites. We have analyzed protein-DNA interactions at the TK promoter during cell cycle progression in human fibroblasts using an in vivo footprinting approach. We found 14 protein binding sites that were occupied in vivo. All of the sites (among them two inverted CCAAT boxes and several Sp1 sites) bound transcription factors constitutively throughout the cell cycle, i.e. none of the factor binding was cell cycle-dependent. An E2F-like site located between nucleotides -97 and -89 relative to the major transcription start site was protected in G0, G1, S, and G2 phases. This cell cycle-independent protection of E2F sequences in the TK promoter differs from the G0/G1-restricted binding of E2F complexes observed for genes in which the E2F sites function as repressor elements (Tommasi, S., and Pfeifer, G. P. (1995) Mol. Cell. Biol. 15, 6901-6913; Zwicker, J., Liu, N., Engeland, K., Lucibello, F. C., and Müller, R. (1996) Science 271, 1595-1597). A comparison of several genes containing E2F motifs indicates that E2F sites located in proximity to the transcription initiation site (-50 to +20) in TATA-less promoters predominantly function as repressor elements, while in other genes constitutively bound E2F complexes located further upstream mediate activation presumably in conjunction with a functional TATA box.
Tommasi
S
S
Department of Biology, Beckman Research Institute, City of Hope National Medical Center, Duarte, California 91010, USA. gpfeifer@smtplink.coh.org
Pfeifer
G P
GP
D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D016384:Consensus Sequence; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000378:metabolism; D050684:E2F Transcription Factors; D005347:Fibroblasts; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics; D056465:Retinoblastoma-Binding Protein 1; D013937:Thymidine Kinase / Q000235:genetics*; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D012333:RNA, Messenger; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D013937:Thymidine Kinase