The ribosomal RNA genes of three salmonid species

The ribosomal RNA cistrons of three species of trout: Salvelinus namaycush (lake trout), Salvelinus fontinalis (brook trout), and Salmo gairdneri (rainbow trout) were examined by Southern blot analysis of genomic DNA. The repeat length of the cistron of S. namaycush is 26 kb. A repeat-length polymorphism was observed in some of the individual fish examined. These individuals showed 24-kb repeats. In some individuals both forms were present. The restriction maps of the transcribed regions of all three species were similar and showed a site homology with other vertebrate ribosomal RNA genes. Interspecific comparison showed restriction-site differences within the spacer regions examined. A restriction-site polymorphism within the 28 S gene was observed in S. fontinalis. The rDNA of S. namaycush liver showed a high degree of methylation as determined by digestion with the restriction endonucleases MspI and HpaII.