Multiple promoter elements including a novel repressor site modulate expression of the chick ovalbumin gene

As is the case with many eukaryotic genes, regulation of the chick ovalbumi n (Ov) gene involves both positive and negative modulation, Recent studies indicate that positive regulation by steroids entails binding of several pr oteins to a hormone-response unit called the steroid-dependent regulatory e lement (SDRE; -892 to -780). In addition, gene activity is suppressed by fa ctor(s) acting through the negative regulatory element (NRE; -308 to -88), Previous data suggested that the NRE is composed of multiple, independently acting negative elements, The goal of the present studies was to define mo re precisely the locations of these negative elements and to investigate th eir functional interactions. Transfection analyses of linker scanning mutan ts revealed a strong repressor site, designated the COUP-adjacent repressor (CAR) site, located between -119 and -111, Gel mobility shift analyses wit h the CAR element suggested that it may play a role in the developmental re gulation of the Ov gene. A weaker repressor element was also identified at about -275, Surprisingly, two positive sites were found, one of which is th e binding site for the estrogen-responsive transcription factor delta-EF1. These results demonstrate that the Ov NRE contains not only sites responsib le for the repression of the gene but also a positive element that is requi red for responsiveness to steroid hormones.