NEGATIVE REGULATION OF THE GENE FOR H-2K(B) CLASS-I ANTIGEN BY ADENOVIRUS 12-E1A IS MEDIATED BY A CAA REPEATED ELEMENT

Both positive and negative regulatory elements responsive to the produ ct of the adenovirus type 12 E1A gene are located in the promoter regi on of the gene for mouse H-2K(bm1) major histocompatibility complex (M HC) class I antigen (1). We have analyzed the negative regulatory elem ent that is affected by E1A and identified a target CAA repeated motif , CAA(A)CAAA, within -1725 to -1705 and -1591 to -1568 in a 316-bp seq uence located in the far upstream region of H-2K(b) promoter (-1837 to -1522; +1 refers to the cap site). The extent of cell surface express ion of the MHC class 1 antigen was significantly decreased in the case of transfectants obtained by introducing an expression plasmid that i ncluded MHC class 1 cDNA with the CAA repeated element, as compared wi th that of a plasmid with mutated CAA repeats. We have also characteri zed the nuclear proteins that bind to this motif. The analysis of the effects of mutations during competition assays of in vivo and gel reta rdation competition assays demonstrated that the CAA repeated element is essential not only for E1A-dependent repression of transcription bu t also for the cell surface expression of the product of the mouse H-2 K(b) class I gene, presumably through nuclear proteins that specifical ly bind to it.