Evidence that fimbriae of the smut fungus Microbotryum violaceum contain RNA.

The cells of the fungus Microbotryum violaceum produce many long, fine surface hairs that are similar in size and morphology to bacterial pili or fimbriae. These fungal fimbriae are assembled from 74 kDa glycoprotein subunits. We now present evidence that these fimbriae also have a RNA component. Isopycnic centrifugation of fimbriae in caesium chloride produced one band at a density intermediate to that of protein and nucleic acid. The absorbance spectrum of the intact fimbriae was consistent with that of a nucleoprotein. After extraneous RNAs were enzymically removed from the purified fimbrial preparation, disruption of the fibrils resulted in the release of not only the 74 kDa glycoprotein subunits, but also a 30 base single-stranded RNA species. To our knowledge, this is the first example of extracellular RNA as a component of a surface appendage.