A cellular repressor regulates transcription initiation from the minute virus of mice P38 promoter.

We previously reported that the P38 promoter of minute virus of mice (MVM) is trans activated by the viral nonstructural protein, NS1, through an interaction with a downstream promoter element designated DPE. In this communication we report the identification of a distinct downstream promoter element which inhibits transcription from the P38 promoter in vitro, in the absence of the DPE. Removal of 34 bp from the region between +95 and +129 downstream from the P38 initiation start site relieved inhibition of transcription in whole-cell extract. Inhibition was also relieved by the addition, to the transcription reaction, of excess DNA fragments which span the putative inhibiting element. This indicated the involvement of a trans-acting factor, in inhibition of transcription from the P38. Gel retardation experiments demonstrated the specific binding of a cellular protein to the inhibitory element. This P38 inhibitory element shows spacing and orientation dependence as well as promoter specificity. The regulation of viral transcription by a cellular repressor may play an important role in obtaining a fine temporal order of viral gene expression during the course of infection.