A common positive trans-acting factor binds to enhancer sequences in the promoters of mouse H-2 and beta 2-microglobulin genes.

Using gel retardation and in vitro "footprinting", we have analyzed the interactions between nuclear proteins derived from various mouse cells and the enhancer and interferon response sequences of the H-2Kb gene. We have found that a protein factor binds a site in the enhancer sequence that partially overlaps the interferon response sequence. This factor also binds to a similar sequence lying in the opposite orientation in the promoter of the mouse beta 2-microglobulin gene, suggesting a common regulatory mechanism. Transfection competition experiments indicate that this factor acts as a positive element in the expression of H-2 and beta 2-microglobulin genes.