A ROLE FOR PHOSPHORYLATION BY CASEIN KINASE-II IN MODULATING ANTENNAPEDIA ACTIVITY IN DROSOPHILA

We present evidence that the in vivo activity of the HOX protein Anten napedia (ANTP) is modified because of phosphorylation by the serine/th reonine kinase casein kinase II (CKII). Using an in vivo assay a form of ANTP that has alanine substitutions at its CKII target sites has, i n addition to wild-type ANTP functions, the ability to alter severely thoracic and abdominal development. The novel functions of this protei n suggest that this form of ANTP is not suppressed phenotypically by t he more posterior homeotic proteins. In contrast, the in vivo activity of a form of ANTP that contains acidic amino acid substitutions at it s CKII target sites, thereby mimicking a constitutively phosphorylated ANTP protein, is greatly reduced. This hypoactive form of ANTP, but n ot the alanine-substituted form, is also reduced in its ability to bin d to DNA cooperatively with the homeodomain protein Extradenticle. Our results suggest that phosphorylation of ANTP by CKII is important for preventing inappropriate activities of this homeotic protein during e mbryogenesis.