MOLECULAR CHARACTERIZATION AND CYTOGENETIC ANALYSIS OF HIGHLY REPEATED DNAS OF LAKE TROUT, SALVELINUS-NAMAYCUSH

The chromosomes of lake trout (Salvelinus namaycush) contain a conside rable amount of heterochromatin located at the centromeres and/or telo meres of several chromosomes, including a sex-specific block located d istally on the X chromosome. In order to investigate further the repet itive DNAs of lake trout, genomic DNA from a female was size fractiona ted (<600 bp) with the restriction endonuclease AluI and fragments wer e cloned into the bacteriophage M13. A total of 42 clones were isolate d. Relative copy number of individual inserts within the lake trout ge nome was estimated by Southern analysis. Twelve clones were determined to be highly repetitive and were chosen for further investigation. In serts of these clones contained sequences similar to the AluI/RsaI, Ec oRI/DraI, DraI/BstEII, and MboI/BglII families reported from Arctic ch ar (Salvelinus alpinus). The chromosomal location of several of these fragments was determined in lake trout by fluorescence in situ hybridi zation (FISH). Two related AluI/RsaI sequences (Type A, similar to 140 bp, and Type B, similar to 120 bp) showed differential hybridization. Type A hybridized to the centromeres of all metacentric as well as se veral acrocentric chromosomes. Type B hybridized to the centromeres of most acrocentric chromosomes. A sequence with homology to the EcoRI/D raI family hybridized to the centromeres of several acrocentric chromo somes. Sequences with partial similarity to the DraI/BstEII family hyb ridized to the major rDNA sites (nucleolar organizer regions, NORs) an d several minor telomeric sites. The interstitial and telomeric hetero chromatin of lake trout, including that of the X chromosome, appears t o comprise sequences belonging to the MboI/BglII family.