Primary and secondary structure of the 25S rRNA from the dimorphic fungus Mucor racemosus.

A 9.76 Kb ribosomal DNA repeat unit from the nuclear genome of the dimorphic fungus Mucor racemosus (Zygomycetes) was identified using a hybridization probe from the yeast Saccharomyces cerevisiae (Ascomycetes). This material was cloned in Escherichia coli plasmids as four overlapping pieces and mapped with respect to cleavage sites for 12 restriction endonucleases. The nucleotide sequence of the complete 25S rRNA gene and flanking regions was determined. The 5' and 3' ends of the structural gene were identified by comparison with the published sequence for the S. cerevisiae gene. The Mucor gene was found to possess 3469 bp and have a GC content of 42.8%. It was compared with the homologous gene from several other eukaryotes and found to be most similar to that from Saccharomyces. A potential secondary structure of the putative RNA transcript consistent with the structures proposed for the E. coli and Saccharomyces molecules was constructed by computer modelling.