The products of the homeotic genes in Drosophila are transcription factors that are necessary to impose regional identity along the anterior-posterior axis of the developing embryo. However, the target genes under homeotic regulation that control this developmental process are largely unknown. We have utilized an immunopurification method to clone target genes of the Antennapedia protein (ANTP). We present here the characterization of centrosomin (cnn), one of the target genes isolated using this approach. The spatial and temporal expression of the cnn gene in the developing visceral mesoderm (VM) of the midgut and the central nervous system (CNS) of wild-type and homeotic mutant embryos is consistent with the idea that cnn is a homeotic target. In the VM, Antp and abdominal-A (abd-A) negatively regulate cnn, while Ultrabithorax (Ubx) shows positive regulation. In the CNS, cnn is regulated positively by Antp and negatively by Ubx and abd-A. Characterization of a cDNA encoding CNN predicts a novel structural protein with three leucine zipper motifs and several coiled-coil domains exhibiting limited homology to the rod portion of myosin. Immunocytochemical results demonstrate that the cnn encoded protein is localized to the centrosome and the accumulation pattern is coupled to the nuclear and centrosome duplication cycles of cleavage. In addition, evidence suggests that the expression of the cnn gene in the VM correlates with the morphogenetic function of Ubx in that tissue, i.e., the formation of the second midgut construction. The centrosomal localization of CNN and the involvement of microtubules in midgut morphogenesis suggest that this protein may participate in mitotic spindle assembly and the mechanics of morphogenesis through an interaction with microtubules, either directly or indirectly.