Context-dependent requirements for DNA-binding by Runt in transcription activation and repression. Michael L. Higgins¹, Lisa Prazak², J. Peter Gergen³. 1) Graduate Program in Biochemistry and Structural Biology, Stony Brook University, Stony Brook, NY. 11794; 2) Graduate Program in Molecular and Cellular Biology, Stony Brook University, Stony Brook, NY 11794-5215; 3) Department of Biochemistry and Cell Biology and the Center for Developmental Genetics, Stony Brook University, Stony Brook, NY 11794-5215.

   The initial metameric expression of the sloppy-paired gene is generated in response to regulatory inputs of the pair rule transcription factors Eve, Ftz, Opa, and Runt. These inputs are integrated by two distinct enhancers, the Distal and Proximal early stripe elements, DESE and PESE. The PESE enhancer is repressed by Runt whereas the DESE enhancer can either be activated or repressed by Runt depending on the absence or presence of Ftz. Here we investigate the effects of mutating binding sites for Runt in reporter gene constructs containing these enhancers. When PESE is tested as an autonomous enhancer we find that mutagenesis of Runt sites results in loss of repression in blastoderm stage embryos. However, this de-repression is not apparent in a composite reporter also containing the DESE enhancer. Similarly, mutation of Runt sites in DESE also results in loss of repression when this element is tested autonomously, but has the opposite effect of interfering with Runt-dependent activation in a composite enhancer that contains PESE. These results are discussed in the context of a model whereby Runt plays a central role in modulating competitive interactions between these two enhancers and the slp1 promoter.