Changes in size and secondary structure of the ribosomal transcription unit during vertebrate evolution

摘要: Abstract Ribosomal RNA and precursor ribosomal from at least one representative of each vertebrate class have been analyzed by electron microscopic secondary structure mapping. Reproducible patterns hairpin loops were found in both 28 S RNA, whereas almost all the 18 molecules lack under spreading conditions used. The species a common design. is located or near presumed 5′-end separated region internal spacer region. In addition there an external 3′-end molecules. Changes length these regions are mainly responsible for increase size during evolution. cold blooded vertebrates contains two short regions; birds bears long region, mammals it has regions. molecular weights, as determined micrographs, 2·6 to 2·8 × 10 6 vertebrates, 3·7 3·9 birds, 4·2 4·7 mammalian precursor. higher proportion when compared lower vertebrates. This observation was confirmed digesting RNAs with single-strandspecific 1 nuclease aqueous solution. Analysis double-stranded, -resistant fragments indicates that direct relationship between seen microscope