[Organization of genes coding for 5S rRNA in the loach Misgurnus fossilis L]

The organization of 5S rRNA genes in the loach Misgurnus fossilis L. was studied. 5S rDNA was cloned in Escherichia coli using the HindIII-fragments of loach genome DNA fused into the plasmid pBR322 restricted at the same site. The recombinant clones were tested by colony hybridization. The presence of the 5S rDNA structural sequences in cloned fragments was determined by the Southern procedure of hybridization with 5S [32P]rRNA of the loach and transcription in the oocyte test system. It was found that the size of 5S rDNA repetitive units corresponds to 240-250 bp and 450-460 bp. By the CsCl centrifugation and restriction analysis it was shown that the 5S genes in the loach genome are arranged in clusters (5-30 repeats per cluster), the smaller repeat was found to contain one coding sequence while the larger repeat contains two coding sequences of 5S rDNA.