FUNCTIONAL REDUNDANCY OF PROMOTER ELEMENTS ENSURES EFFICIENT TRANSCRIPTION OF THE HUMAN 7SK GENE IN-VIVO

Deletion and mutation studies of the human 7SK gene transfected into H eLa cells have identified three functional regions of the promoter cor responding to the TATA box at -25, the proximal sequence element (PSE) between -49 and -65 and the distal sequence element (DSE) between -24 3 and -210. These elements show sequence homology to equivalent region s in other snRNA genes and are functionally analogous. Unlike the DSEs of many snRNA genes however, the 7SK DSE does. not contain a consensu s binding site for the transcription factor Oct-1 but rather, contains two non-consensus Oct-1 binding sites that can function independently of one another to enhance transcription. Unusually, the 7SK PSE can r etain function even after extensive mutation and removal of the conser ved TGACC of the PSE has little effect in the context of the whole pro moter. However, the same mutation abolishes transcription in the absen ce of the DSE suggesting that protein/protein interactions between DSE and PSE binding factors can compensate for a mutant PSE. Mutation of the 7SK TATA box allows snRNA type transcription by RNA polymerase II to occur and this is enhanced by the DSE, indicating that both the DSE and the PSE can also function with pol II. In addition, mutation of t he TATA box does not abolish pol III dependent transcription, suggesti ng that other sequence elements may also play a role in the determinat ion of polymerase specificity; Although the human 7SK gene is transcri bed efficiently in Xenopus oocytes, analysis of the 7SK wild-type gene and mutants in Xenopus oocytes gives significantly different results from the analysis in HeLa cells indicating that the recognition of fun ctional elements is not the same in the two systems. (C) 1995 Academic Press Limited