A developmentally regulated trans-acting factor recognizes dissimilar G/C-rich elements controlling a class of cAMP-inducible Dictyostelium genes.

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Abstract
Transcriptional response elements involved in the cAMP-inducible and developmentally regulated expression of the Dictyostelium aggregate-stage gene pst-cath/CP2 have been shown to include a G/C-rich sequence element [G-box regulatory element (GBRE)]. We have recently identified a trans-acting factor, GBF (GBRE binding factor), that specifically interacts with this sequence and have shown that the binding activity of GBF to GBRE is developmentally regulated and inducible by cAMP. Here, we examine further the possible role of GBF in the regulation of pst-cath/CP2 and three other coordinately regulated, cAMP-inducible aggregate-stage genes. We show that GBF itself (or other closely related factors) recognizes dissimilar G/C-rich elements present in the 5'-flanking regions of these genes and that the ability of the individual, distinct G/C-rich elements to confer regulated expression on a promoter deletion mutant of the pst-cath/CP2 gene is correlated with the relative affinity for GBF. G/C-rich elements carrying point mutations that prevent in vitro binding of GBF to two of the G/C-rich elements fail to activate expression in vivo. An analysis of major points of contact between the GBF protein and two distinctly different binding sites suggests that binding of GBF to these sequence elements involves a considerable degree of flexibility in DNA-protein interactions. These results suggest that the regulated expression of a class of aggregate-stage cAMP-inducible genes involves the interaction of GBF or homologous factors with dissimilar G/C-rich sequence elements and that induction of GBF activity or that of homologous factors by cAMP may thus be a limiting step in the induction of this temporally coordinate set of genes during Dictyostelium development.