CONCENTRATION-DEPENDENT TRANSCRIPTIONAL ACTIVATION OR REPRESSION BY KRUPPEL FROM A SINGLE BINDING-SITE

ONE of the gap class of segmentation genes 1, Kruppel (Kr), is required for normal thorax and abdominal development of the Drosophila embryo. Its gene product, a zinc-finger type protein 2, forms a bell-shape concentration gradient in a central position of the blastoderm 3-6. Genetic and molecular studies suggested that the Kr protein (KR) may act both as a positive and as a negative regulator of transcription on several other genes 3-9 of the zygotic segmentation hierarchy 1. We have examined the regulatory potential of Kr by a series of cotransfection experiments in the Drosophila Schneider cell line system. Different doses of Kr expression plasmid were tested for their ability to drive reporter gene expression mediated by a single 11-base pair KR in vitro binding site common to several putative Kr target genes 4-6,8-10. Our results show that low amounts of Kr expression plasmid lead to transcriptional activation, whereas high amounts result in repression. Distinct portions of KR other than the DNA-binding domain are required for gene activation and repression, suggesting that KR itself can act as a concentration-dependent positive and negative regulator of transcription.