The nucleotide sequence of the intergenic region between the 5.8S and 26S rRNA genes of the yeast ribosomal RNA operon. Possible implications for the interaction between 5.8S and 26S rRNA and the processing of the primary transcript

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Abstract
We have determined the nucleotide sequence of part of a cloned yeast ribosomal RNA operon extending from the 5.8S RNA gene downstream into the 5′-terminal region of the 26S RNA gene. We mapped the pertinent processing sites, viz. the 5′ end of 26S rRNA and the 3′ ends of 5.8S rRNA and its immediate precursor, 7S RNA. At the 3′ end of 7S RNA we find the seguence UCGUUU which is very similar to the type I consensus sequence UCAUU A /U present at the 3′ ends of 17S, 5.8S and 26S rRNA as well as 18S precursor rRNA in yeast. At the 5′ end of the 26S RNA gene we find a sequence of thirteen nucleotides which is homologous to the type II sequence present at the 5′ termini of both the 17S and the 5.8S RNA gene. These findings further support the suggestion put forward earlier (G.M. Veldman et al. (1980) Nucl. Acids Res. 8, 2907-2920) that both consensus sequences are involved in the recognition of precursor rRNA by the processing nuclease(s). We discuss a model for the processing of yeast rRNA in which a processing enzyme sequentially recognizes several combinations of a type I and a type II consensus sequence. We also describe the existence of a significant base complementarity between sequences in the 5′-terminal region of 26S rRNA and the 3′-terminal region of 5.8S rRNA. We suggest that base pairing between these sequences contributes to the binding between 5.8S and 26S rRNA.