REPRESSION MECHANISMS OF THE I-A-BETA GENE OF THE MAJOR HISTOCOMPATIBILITY COMPLEX

The mechanisms of regulation of I-AP gene expression in the murine maj or histocompatibility complex by transcriptional repression are review ed. Active and passive repression mechanisms are presented. The transc ription factor PU.1 actively inhibits the expression of I-AP through t he binding to a DNA sequence near the Y box, a cis-element in the prom oter necessary for transcription. This interaction probably interferes with the preinitiation complex assembly. NF-Y is a transcription fact or that binds to the Y box and has two constituents: NF-YA (that binds weakly to DNA) and NF-YB (that increases I:he binding of NF-YA to DNA ). The dbpA protein represses the expression of I-A beta by a quenchin g mechanism, forming a complex with NF-YA and the dbpB protein by sequ estering the NF-YB protein. PI similar mechanism is observed with the glucocorticoid receptor that binds to the X-box binding proteins and i nhibits their interaction with the X box. These results are examples o f cross-talk between proteins, which may help us to understand the reg ulation of 1-A beta gene expression.