Isolation and characterization of cytochrome c from the marine copepod Tigriopus californicus

Mitochondrial energy production requires complex interactions among protein s encoded in both the nuclear and mitochondrial genomes. The intergenomic c oevolution of interacting gene products has been previously suggested based on interspecific comparisons of cytochrome c (encoded by the nuclear CYC g ene) and cytochrome c oxidase (partly encoded in the mitochondrial DNA by t he COX1, COX2 and COX3 genes). In the intertidal copepod, Tigriopus califor nicus, non-synonymous substitutions in the COX1 gene have previously been f ound in interpopulation comparisons. Tn order to determine if CYC also show s interpopulation variation, this gene was isolated from a cDNA library usi ng a degenerate primer/polymerase chain reaction approach. Characterization of a cDNA sequence and 25 genomic DNA sequences derived from four T. calif ornicus populations yielded the following results: (1) the T. californicus CYC gene is interrupted by an intron that occurs at the same position as th e intron found in vertebrate CYC genes; (2) there is extensive sequence var iation within both the coding region and intron of this gene and the vast m ajority of this variation occurs between sequences drawn from geographicall y distinct populations; (3) the coding sequence variation includes a minimu m of five amino acid replacement substitutions; (4) segregation of length v ariants among offspring in an interpopulation cross revealed genotypic rati os consistent with the proposed allelic nature of the CYC variants. These r esults demonstrate that the requisite genetic variation required for interg enomic coevolution exists in the CYC-COX system in T. californicus. (C) 200 0 Elsevier Science B.V. All rights reserved.