Drosophila Krüppel gene product produced in a baculovirus expression system is a nuclear phosphoprotein that binds to DNA.

The product of the Drosophila segmentation gene Krüppel was produced in cultured insect cells using the baculovirus expression system. When a cloned Krüppel cDNA sequence was inserted into the viral genome downstream from the promoter of the polyhedrin gene, a polypeptide with an apparent molecular weight of approximately equal to 72,000 was observed in the nuclei of infected cells. Antibodies were raised against this protein and used to detect Krüppel in Drosophila embryos. Characterization of the Krüppel protein extracted from infected cells showed that it is tightly bound to the nucleus, it binds to calf thymus DNA-cellulose, and it is phosphorylated. These results support the hypothesis that Krüppel is a regulatory protein that acts by binding DNA.