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KMID : 0903519900330020000
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Journal of the Korean Society of Agricultural Chemistry and Biotechnology
1990 Volume.33 No. 2 p.0 ~ p.0
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Primary and secondary structure of the 25 S rRNA from the Dimorphic Fungus Mucor racemosus
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Abstract
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A 9.76-Kb ribosomal DNA repeat unit from the nuclear genome of the dimorphic fungus Mucor racemosus (zygomycetes) was cloned into E. call plasmids as four overlapping pieces and mapped. The nucleotide sequence of the complete 25s rRNA gene and flanking regions were determined. The 5´ and 3´ ends of the structural gene was identified by comparison with the published sequence for the S. cerevisiae gene. The Mucor gene was found to posses 3469 by compared with 3392 by in the Saccharomyces gene. The main reason for this difference is the apparent insertion of a 106-by segment(from bp-608 to bp-713) in the Mucor gene. This 106-by segment having a GC content of only 37%, departs radically from the typical GC-rich insertion sequences found in the gene of higher eukaryotes. Indeed the entire 25S rRNA gene from Mucor has a very low content (42.8%) compared with homologous gene from other eukaryotes. Saccharomyces and Drosophila were the only other organisms for which this value has been reported below 50%.
The Saccharomyces 25S rRNA molecule is post-transcriptionally methylated at 43 sites, 30 of which have been identified in the base sequence by Veldman et al.. Our sequence data indicated that all 30 sites were conserved in Mucor gene. Moreover, 750 bp immediately surrounding the 30 methylation sites showed 98% sequence similarity with the gene from Saccharomyces.
By means of computer-assisted modeling, we were able to organize the 25S rRNA from Mucor into seven domains that are clearly homologous with the established domains in the molecules from E. coli and Saccharomyces. The stem and loop structure are generally similar, though nor always identical to the E. coli-Saccharomyces paradigm. The inserted 106bp segment is found in domain II as part of a highly stable stem-loop structure. Domain VII contains a loop with a base sequence identical to the alpha-sarcin cleavage site located in homologous regions of both E. coli 23S rRNA and Saccharomyces 25S rRNA. Even those domains (II and VII) in which sequence similarity to that of Saccharomyces was its lowest secondary structure was substantially conserved.
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