AN ALUI FRAGMENT ISOLATED FROM LAKE TROUT (SALVELINUS-NAMAYCUSH), MAPS TO THE INTERGENIC SPACER REGION OF THE RDNA CISTRON

The relationship between a 217-bp AluI fragment (SnAluI-33c) from lake trout (Salvelinus namaycush) which hybridizes to the nucleolar organi zer regions (NORs) and the ribosomal RNA genes was examined by Souther n analysis and comparative hybridization. Restriction enzymes with rec ognition sites mapped in the lake trout rDNA cistron were used to dige st genomic DNA into fragments of predetermined size. Comparison of the hybridization pattern of SnAluI-33c with those of two rDNA-specific p robes placed this fragment within the intergenic spacer region of the rDNA cistron, approximately 3 kb upstream (5') of the 18S gene. This f inding is consistent with in situ hybridization experiments showing hy bridization of this fragment to sites of rDNA [Reed, K.M. and Phillips , R.B., Cytogenet. Cell Genet. 70 (1995) 104-107]. Based on cross hybr idization and sequence comparisons, homologous sequences are present i n other salmonid species.