title: Structure and expression of rodent genes encoding the testis-specific cytochrome c. Differences in gene structure and evolution between somatic and testicular variants.
abstract: Mammalian testis contains two forms of cytochrome c, one identical to the form found in somatic tissues and a second that is expressed in a stage-specific manner during spermatogenic differentiation. We have isolated both rat and mouse cDNA clones and the rat gene encoding the testis-specific cytochrome c and determined their DNA sequences. The testicular variant displays a number of notable differences with its somatic counterpart. 1) In contrast to the multipseudogene family derived from mammalian somatic cytochrome c genes, the testis gene is single-copy in genomic DNA with no detectable pseudogenes. 2) The rat testis gene is approximately 7 kilobases (kb) long with three introns totaling nearly 6.5 kb whereas the two introns dividing the 2.1-kb somatic gene occupy only 0.9 kb. Introns differ in position as well as size. 3) The testicular variant has a longer 5'-untranslated leader (230 versus 70 base pairs for the somatic gene) with an upstream open reading frame of 129 base pairs beginning with an AUG in a favorable translational context. 4) A single polyadenylation site in the testicular mRNA (approximately 900 nucleotides) contrasts with the three functionally equivalent sites observed in rat somatic messages. 5) Finally, rat and mouse testis cytochromes c differ at 4 amino acid residues as opposed to the complete sequence identity found in the somatic proteins suggesting a shorter unit evolutionary period for these molecules. These observations are consistent with a duplication of an ancestral cytochrome c gene leading to the emergence of novel structural features and regulatory properties likely associated with the striking tissue specificity of the testicular cytochrome c.
authors.affiliation: Department of Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611.
authors.forename: J V
authors.initials: JV
authors.lastname: Virbasius
authors.forename: R C
authors.initials: RC
authors.lastname: Scarpulla
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D003574:Cytochrome c Group / Q000235:genetics*; D005796:Genes; D014644:Genetic Variation; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009710:Nucleotide Mapping; D009928:Organ Specificity; D051381:Rats; D013737:Testis / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D003574:Cytochrome c Group