A divergent cDNA homologue of the c-myc proto-oncogene in the eastern oyster Crassostrea virginica: implications for Myc evolution.
The polymerase chain reaction was used to identify myc-like cDNA fragments from several marine invertebrate phyla. A PCR clone produced from the eastern oyster Crassostrea virginica was subsequently used to screen a larval cDNA library, and a 1.9-kb cDNA clone was isolated and sequenced. The putative amino acid sequence encoded by this clone evidences a leucine zipper at its predicted carboxyl-terminus and has an overall structural similarity to vertebrate c-myc proto-oncogenes with several regions of high amino acid similarity. However, this oyster cDNA clone lacks the necessary amino acid conservation in the critical functional domains of Myc and thus is unlikely to function intracellularly in the oyster as a true homologue of vertebrate c-myc. We propose that the oyster cDNA clone described here represents a gene that has been derived from the same ancestral gene that eventually gave rise to vertebrate c-myc. Despite the apparent critical importance of the c-myc proto-oncogene in regulating cellular activities, these data suggest that the c-myc gene: (1) is unique to deuterostome phyla, and (2) assumed its critical role in regulating cell cycle activities at the divergence of the deuterostome ancestors from other protostomes during the Cambrian explosion. In support of these conclusions we present a functional model for the evolution of the Myc gene.
Marsh
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Center of Marine Biotechnology, Maryland Biotechnology Institute, University of Maryland System, Baltimore 21202, USA.
Chen
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D018076:DNA, Complementary / Q000235:genetics; D016259:Genes, myc / Q000235:genetics*; D007448:Invertebrates / Q000235:genetics; D016350:Leucine Zippers; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010125:Ostreidae / Q000235:genetics*; D017433:Protein Structure, Secondary; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D014714:Vertebrates / Q000235:genetics
D018076:DNA, Complementary; D016271:Proto-Oncogene Proteins c-myc