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, throu gh an interaction with a downstream promoter element designated DPE. I n this communication we report the identification of a distinct downst ream promoter element which inhibits transcription from the P38 promot er in vitro, in the absence of the DPE. Removal of 34 bp from the regi on 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 t ranscription from the P38. Gel retardation experiments demonstrated th e specific binding of a cellular protein to the inhibitory element. Th is 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 t emporal order of viral gene expression during the course of infection.