TARGETING OF PROMOTERS FOR TRANS ACTIVATION BY A CARBOXY-TERMINAL DOMAIN OF THE NS-1 PROTEIN OF THE PARVOVIRUS MINUTE VIRUS OF MICE

The NS-1 gene of the parovirus minute virus of mice (MVM) (prototype s train, MVMp) was fused in phase with the sequence coding for the DNA-b inding domain of the bacterial LexA repressor. The resulting chimeric protein, LexNS-1, was tested for its transcriptional activity by using various target promoters in which multiple LexA operator sequences ha d bee introduced. Under these conditions. NS-1 was shown to stimulate gene expression driven by the modified long terminal repeat promoters (from the retroviruses mouse mammary tumor virus and Rous sarcoma viru s) and P38 promoter (from MVMp), indicating that the NS-1 protein is a potent transcriptional activator. It is noteworthy that in the absenc e of LexA operator-mediated targeting, the genuine mouse mammary tumor virus and Rous sarcoma virus promoters were inhibited by NS-1. Togeth er these data strongly suggest that NS-1 contains an activating region able to induce promoters with which this protein interacts but also t o repress transcription from nonrecognized promoters by a squelching m echanism similar to that described for other activators. Deletion muta nt analysis led to the identification of an NS-1 domain that exhibited an activating potential comparable to that of the whole polypeptide w hen fused to the DNA-binding region of LexA. This domain is localized in the carboxy-terminal part of NS-1 and corresponds to one of the two regions previously found to be responsible for toxicity. These result s argue for the involvement of the regulatory functions of NS-1 in the cytopathic effect of this parovirus product.