A complete copy of Ki-ras b
cDNA from English sole (Pleuronectes vetulus), a benthic marine flatfish, was cloned and sequenced. The percent identity between the predicted amino acid sequence of English sole and human Ki-ras b was 97%, whereas the percent identity between the English sole gene and rainbow trout or Rivulus Ki-ras b was 98%. Areas of amino-acid sequence conservation included
codons 12, 13, and 61, the positions in which mutations are observed in ras cellular oncogenes in other species. The
5' untranslated region (UTR), consisting of 217 nt, was not highly GC rich but contained four ATG
start codons upstream of the major open reading frame. The
3' UTR, containing 26 nt, was AU rich. Analysis of Ki-ras mutations was performed on a variety of necrotic, preneoplastic, and neoplastic lesions in livers from 13 English sole collected from contaminated waterways in Puget Sound, WA. Despite reports of Ki-ras mutations in hepatic
tumors from other fish, no mutations in
codons 12, 13, or 61 were found in hepatic lesions from English sole by direct
DNA sequencing of polymerase chain reaction-amplified genomic
DNA. Although mutations could exist at levels below the detection limits of this analysis, the results suggest that Ki-ras has a role in liver
carcinogenesis that varies according to the fish species or
carcinogen. Furthermore, future studies of the etiology of chemically induced
cancer in
feral English sole should consider mutations in other
cancer-related genes, such a5p53, Ha-ras, and N-ras.