PHOSPHORYLATION OF THE DROSOPHILA ENGRAILED PROTEIN AT A SITE OUTSIDEITS HOMEODOMAIN ENHANCES DNA-BINDING

The engrailed gene encodes a homeodomain-containing phosphoprotein tha t binds DNA. Here, we show that engrailed protein is posttranslational ly modified in embryos and in embryo derived cultured cells but is ess entially unmodified when expressed in Escherichia coil, Engrailed prot ein produced by bacteria can be phosphorylated in nuclear extracts pre pared from Drosophila embryos, and phosphotryptic peptides from this m odified protein partly reproduce two-dimensional maps of phosphotrypti c fragments obtained from metabolically labeled engrailed protein. The primary embryonic protein kinase modifying engrailed protein is casei n kinase II (CK-II), Analysis of mutant proteins revealed that the in vitro phosphoacceptors are mainly clustered in a region outside the en grailed homeodomain and identified serines 394, 397, 401, and 402 as t he targets for CK-II phosphorylation. CK-II-dependent phosphorylation of an N-truncated derivative of engrailed protein purified from bacter ia increased its DNA binding 2-4-fold.