INTRAINDIVIDUAL AND INTERSPECIES VARIATION IN THE 5S RDNA OF COREGONID FISH

This study was designed to characterize further the nontranscribed int ergenic spacers (NTSs) of the 5S rRNA genes of fish and evaluate this marker as a tool for comparative studies. Two members of the closely r elated North American Great Lakes cisco species complex (Coregonus art edi and C. zenithicus) were chosen for comparison. Fluorescence in sit u hybridization found the ciscoes to have a single multicopy 5S locus located in a C band-positive region of the largest submetacentric chro mosome. The entire NTS was amplified from the two species by polymeras e chain reaction with oligonucleotide primers anchored in the conserve d 5S coding region. Complete sequences were determined for 25 clones f rom four individuals representing two discrete NTS length variants. Se quence analysis found the length variants to result from presence of a 130-bp direct repeat. No two sequences from a single fish were identi cal. Examination of sequence from the coding region revealed two types of 5S genes in addition to pseudogenes. This suggests the presence of both somatic and germline (oocyte) forms of the 5S gene in the genome of Coregonus. The amount of variation present among NTS sequences ind icates that accumulation of variation (mutation) is greater in this mu lticopy gene than is gene conversion (homogenization). The high level of sequence variation makes the 5S NTS an inappropriate DNA sequence f or comparisons of closely related taxa.