HIV Tat represses transcription of the beta(2)-microglobulin promoter

The MHC class I complex, which binds and presents peptide antigen, is compo sed of a class I heavy chain and the beta(2)-microglobulin light chain. HIV -1, which induces a profound immunodeficiency in infected individuals, enco des proteins that cause decreased expression of class I heavy chain. We now report that the HIV Tat protein, which is a potent transactivator of viral transcription, is also a potent repressor of the beta(2)-microglobulin gen e. Repression is mediated through the basal promoter of the beta(2)-microgl obulin gene, which is shown to be predominantly regulated by an initiator e lement. Tat repression is further augmented by the short viral transcript, TAR, which interacts with Tat. Tat-mediated repression of beta(2)-microglob ulin expression, together with its known repression of class I gene transcr iption, provides an effective mechanism by which HIV could prevent cell sur face expression of the MHC class I complex and avoid immune surveillance. P ublished by Elsevier Science Ltd.