Organization of the Ribosomal Genes Cluster of the Loach
Ribosomal DNA was prepared from the nucleoli of the loach oocytes. The nucleoli were isolated by the differential centrifugation of homogenates from small growth oocytes and from oocytes at the beginning of vitellogenesis. DNA samples were analysed by density gradient centrifugation and hybridization with labeled rRNA of loach. The samples were enriched 200–300-fold in ribosomal RNA genes. rDNA was digested with EcoRI, Bam H1 and Hind III nucleases and analysis of the restricts by gel electrophoresis was carried out. The Eco R1 and Bam H1 nucleases were shown to have only one restriction site in rDNA of loach amplified nucleoli. The Hind III nuclease has at least five restriction sites. The combination of Eco R1 and Bam H1 nucleases cleaves this rDNA into two fragments of 6.1 and 3.7×106 daltons. The data indicate that the ribosomal RNA gene of loath has a repeat unit of 9,8×106 daltons and is not heterogeneous in the length.
KeywordsDouble Digestion Ribosomal Operon Saturated Phenol CsCl Density Gradient Yolk Oocyte
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