Inactivation of MED-1 elements in the TATA-less, initiator-less mouse thymidylate synthase promoter has no effect on promoter strength or the complexpattern of transcriptional start sites

The mouse thymidylate synthase (TS) promoter is a member of a family of pro moters that lack a TATA box as well as an initiator element and that initia te transcription at many sites over a broad initiation window. An element ( MED-1) downstream of the initiation window of almost all promoters of this family has been proposed to be important for promoter activity, as well as for multiple start site utilization. Two consensus MED-1 elements are locat ed downstream of the initiation window of the TS promoter. To determine the role of the MED-1 elements in the TS promoter, one or both elements were i nactivated by site-directed mutagenesis and the effects on promoter functio n were determined. We found that inactivation of the MED-1 elements had no measurable effect on promoter strength, the boundaries of the initiation wi ndow, or the pattern of transcriptional start sites. Furthermore, inactivat ion of the elements did not affect the ability of the TS promoter to direct S phase-specific expression of the gene in growth-stimulated cells. We con clude that the MED-1 element does not play a significant role in TS promote r function and therefore is not an essential component of all TATA-less pro moters with complex transcriptional initiation patterns. J. Cell. Biochem. 73:90-96, 1999. (C) 1999 Wiley-Liss, Inc.