Synergistic activation of the TATA-less mouse thymidylate synthase promoter by the Ets transcription factor GABP and Sp1.

The mouse thymidylate synthase (TS) promoter lacks a TATA box and an initiator element and directs transcriptional initiation at multiple sites over a 90-nucleotide region. The minimum sequence required for wild-type promoter activity has been mapped to a 30-nucleotide essential promoter region that partially overlaps the 5' end of the transcriptional initiation window. The essential promoter region contains two potential binding sites for members of the Ets family of transcription factors as well as a binding site for Sp1. Promoter mutation analyses revealed that all three of these sites are important for promoter activity. Transient cotransfection assays showed that GABP, a heterodimeric Ets factor, is able to stimulate expression of reporter genes driven by the wild-type mouse TS promoter whereas several other Ets factors have no effect. Electrophoretic mobility shift assays revealed that recombinant GABP binds to both Ets elements in the essential promoter region. Stimulation of promoter activity by GABP is diminished when either Ets element is inactivated and is prevented when both Ets elements are inactivated. Transient cotransfection assays revealed that Sp1 and GABP stimulate TS promoter activity in a highly synergistic manner.

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