T-CELL-SPECIFIC PROTEIN-DNA INTERACTIONS OCCURRING AT THE CD4 LOCUS - IDENTIFICATION OF POSSIBLE TRANSCRIPTIONAL CONTROL ELEMENTS OF THE MURINE CD4 GENE

The cis-acting transcriptional control elements of the murine CD4 gene were investigated within 75 kb of chromatin associated with the CD4 locus. DNase I hypersensitive (DH) sites were identified in several T and non-T cell lines, and in freshly isolated thymocytes. A total of 22 DH sites were found, seven of which are present only in T cells expressing CD4 or CD8. The T cell-specific DH sites are located in four regions: (i) 5' of the first exon of CD4, (ii) in the first intron, (iii) near the second and third exons, and (iv) 3' of the CD4 gene. Some of these sites inversely correlate to the CD4 expression at defined stages of T cell development, suggesting a role for these sites in repression of this gene. The T cell-specific DH sites were subcloned and analyzed for protein - DNA interactions using the electrophoretic mobility shift assay. All T cell-specific DH sites analyzed appear to be a consequence of T cell-specific protein - DNA interactions. We have also identified the nuclear matrix attachment regions (MARs) and repetitive elements associated with the CD4 gene. Two nuclear MARs, separated by a region of highly repetitive DNA, are located 5' of the gene. Another region of highly repetitive DNA exists within the third intron. We discuss the implications of our results for the developmental regulation of CD4 expression.