THE CHROMATIN STRUCTURE OF THE MOUSE BETA-2-MICROGLOBULIN LOCUS

Within the promoter regions of both major histocompatibility complex (MHC) class I genes and the beta2-microglobulin (beta2m) gene, there are a number of common regulatory elements suggesting co-ordinate control. However, there is also evidence to suggest that beta2m and class I are differentially regulated, indicating that these genes may have distinct regulatory elements. We sought to explore this question by analysing DNase I hypersensitive (DH) sites flanking the beta2m gene. Five DH sites have been found within the vicinity of the beta2m gene. One of these sites (DH1) located within the promoter region, correlates with the transcriptional activity of beta2m since it is weak in embryonal (beta2m negative) cell lines. The remaining DH sites (2-5) are located downstream of the beta2m gene. The most proximal downstream site, (DH2) located 5.5 kb from the last exon, was observed only in embryonal cell lines, indicating possible involvement in the downregulation of beta2m. Furthermore, this site is markedly diminished in differentiated F9 cells. Possible roles for the remaining sites are discussed, in particular relationship to a second transcriptional unit identified in the vicinity. In addition, a similar analysis reveals a cluster of DH sites located downstream from the last exon of the human beta2m gene.