Molecular characterization of two myb-related genes in Caenorhabditis elegans,

Two myb-related genes (RI578 and RI838) have been isolated from the Caenorhabditis elegans genome by hybridization using the myb DNA fragment of the avian myeloblastosis virus under low stringency conditions. Southern hybridization indicated that both genes are single copy. Northern hybridization revealed that the RI578 gene encodes three mRNA transcripts (3.2 kb, 2.7 kb and 1.5 kb), which are predominantly expressed at late L1 and early L2 larval stages. Nearly full length cDNA clones corresponding to 3.2 kb and 1.5 kb transcripts (cd578 and cd579) have been isolated and sequenced. Sequence comparison of the cDNA clones illustrated that they appear to be generated by alternative splicing. Predicted protein sequences from cDNA show that the two cDNA clones encode structurally different proteins: a myb-related protein (cd578) that shows 38% sequence similarity to the myb protein at the amino acid level; and a membrane protein (cd579) that shares sequence homology (38%) with yeast ATP/ADP carrier protein. The myb-related protein was localized in germ line cells by indirect immunofluorescence staining using affinity purified polyclonal antibodies. RI838 is also a single copy gene and encodes a 2.8 kb transcript that is expressed selectively in early L1 larvae. A 2.5 kb cDNA clone of this gene has been isolated and sequenced. Sequence analysis shows that it encodes a protein of 600 amino acid residues. The N-terminal protein sequence shows weak similarities to both myb and fos protein. Hydropathy analysis of the protein structure reveals a hydrophobic domain of 40 amino acid residues in the middle of the protein followed by a group of basic amino acids. The RI838 gene shows virtually no sequence similarity to the myb-related transcript cd578. The gene has been mapped onto the X-chromosome near the sma-5 locus by both in situ hybridization and deficiency mapping. Western blot and indirect immunofluorescence staining with the affinity purified antibody show that the gene product is expressed in L1 larvae as a 66 kilo-dalton protein and that it is localized in the pharynx exclusively.