Repression by Knirps: dCtBP dependent and independent activities. D. Arnosti , M. Kulkarni , P. Struffi , Y. Mao , S. Keller. Dept Biochemistry, Michigan State Univ, East Lansing, MI.

   The Knirps repressor is a zinc-finger transcription factor that regulates gap and pair-rule gene expression in the early embryo. Knirps is a "short-range" repressor that can interact with promoter or enhancer elements located within 100 bp of Knirps binding sites. The protein binds to the dCtBP co-repressor via a short motif P-DLS-K, and mutations in dCtBP severely compromise Knirps activity (Nibu et al. (1998) EMBO J. 17, 7009). Using transgenic embryo assays, we find that Knirps contains a separate N-terminal repression domain that is independent of the dCtBP binding region, suggesting that Knirps uses multiple pathways to mediate transcriptional repression. The Knirps DNA binding domain may also play a role in regulation of Knirps repression activity; in the context of the full-length Knirps protein, the loss of dCtBP binding inhibits repression activity, while chimeric proteins that contain a heterologous DNA binding domain can still repress via the N-terminal repression domain. We are currently characterizing the basis of this potential allosteric control. Putative targets of the non-dCtBP interacting N-terminal repression domain identified in biochemical and genetic screens will also be discussed.