Unusual organization and lack of recombination in the ribosomal RNA genes of Coprinus cinereus

Abstract
We find three interesting characteristics of the genes encoding the ribosomal RNA (rRNA) in the basidiomycete Coprinus cinereus. First, there are only 60 to 90 copies of the genes, fewer than in other fungi. Second, the genes are organized in an unusual arrangement. The 5S rRNA genes are located in the repeat unit which encodes the other rRNAs and all four rRNAs are transcribed in the same direction. Third, meiotic recombination is inhibited within the ribosomal DNA.