| We show here that steroid receptor coactivator 1 ( SRC 1 ) is a coactivator of MHC class 2 genes that stimulates their interferon gamma ( IFNgamma ) and class 2 transactivator ( CIITA ) mediated expression . ^^^ SRC 1 interacts physically with the N terminal activation domain of CIITA through two regions : one central [ extending from amino acids ( aa ) 360 839 ] that contains the nuclear receptors binding region and one C terminal ( aa 1138 1441 ) that contains the activation domain 2 . ^^^ We provide evidence that inhibition by estradiol is due to multiple events such as slightly reduced recruitment of CIITA and SRC 1 and severely inhibited assembly of the preinitiation complex . . ^^^ |