THE PUTATIVE CELL-CYCLE GENE, ENHANCER OF RUDIMENTARY, ENCODES A HIGHLY CONSERVED PROTEIN FOUND IN PLANTS AND ANIMALS

The enhancer of rudimentary gene, e(r), in Drosophila melanogaster enc odes a protein, ER, whose function has been implicated in pyrimidine b iosynthesis and the cell cycle (Wojcik et al. (1994) Genetics 138, 116 3-1170). In order to identify conserved regions of the protein and pot entially important functional domains, the e(r) gene was cloned and se quenced from two other insects (Drosophila virilis and Aedes aegypti) and three vertebrates (Homo sapiens, Mus musculus, and Brachydanio rer io) and sequenced from a flowering plant (Arabidopsis thaliana). These sequences along with those of a nematode (Caenorhabditis elegans) exh ibit a high degree of identity. ER of Drosophila melanogaster is 76% i dentical to the three vertebrate proteins, 49% identical to the nemato de protein, and 40% identical to the plant protein. There is high evol utionary conservation among the vertebrates. The mouse and human prote ins are identical and differ from that of the zebrafish by a single co nservative amino-acid change (valine for isoleucine). A dramatic seque nce conservation is seen in the position of the hydrophobic amino acid s. Of the 27 positions occupied by hydrophobic amino acids in ER of Dr osophila melanogaster, 25 of the corresponding positions in the human protein, 23 of the positions in Caenorhabditis elegans, and 20 of the positions in Arabidopsis thaliana have hydrophobic amino acids. Most o f these residues are present in three conserved amphipathic a-helices, which are proposed to function in protein-protein interactions. Two p hosphorylation sites for casein kinase II (CKII) have also been conser ved within the animal groups. Purified ER from Drosophila melanogaster is phosphorylated in vitro by CKII, arguing that these two sites are functional in vivo. A putative shift in the secondary structure of ER caused by the phosphorylation of these sites suggests that CKII may be regulating the activity of the ER in vivo.