ETS-1 ACTIVATES THE DRA PROMOTER IN B-CELLS

The X box in promoters of class II major histocompatibility complex ge nes plays a crucial role in the B-cell-specific and gamma interferon-i nducible expression of these genes. The sequence TTCC is located in th e pyrimidine tract which extends 5' to and partially overlaps the X bo x of the DRA promoter. This sequence resembles the core binding site f or the Ets family of DNA-binding proteins. In this study, we demonstra te that mutations within the pyrimidine tract which change the TTCC mo tif, but do not affect the binding of regulatory factor X to the X box , decrease the activity of the DRA promoter in B cells. Furthermore, u sing electrophoretic mobility shift assays and cotransfection experime nts, we demonstrate that Ets-1, but not Ets-2 or PU.1, functionally in teracts with the pyrimidine tract and activates the DRA promoter.