Drosophila Krüppel protein is a transcriptional repressor

Krüppel (Kr), one of the zygotically active Drosophila segmentation genes, is expressed in a restricted domain during the blastoderm stage of embryogenesis and is involved in the control of development of the thoracic and abdominal segments of the fly. Kr encodes a polypeptide containing DNA-binding zinc-finger motifs, disruptions of which yield Kr mutants. We have assayed the transcriptional activities of wild-type Kr protein as well as Lac repressor/Kr fusion proteins in HeLa and CV-1 cells. Wild-type Kr and a Lac-Kr chimaeric protein repressed transcription from reporter promoters in which a consensus Kr binding site derived from sequences within the even-skipped promoter had been inserted in an upstream position. We mapped the repression function of Kr to an alanine-rich amino-terminal region of the protein, as a Lac/Kr fusion protein containing only amino acids 26-110 of Kr repressed transcription from a reporter promoter containing upstream lac operators. This demonstrates that the DNA-binding and repression activities of the Kr protein are distinct. These data are consistent with genetic evidence that Kr represses even-skipped and hunchback expression, and suggest that Kr is a negative regulator of transcription in Drosophila.