RIBOSOMAL-RNA MOLECULAR-WEIGHTS OF TRICHOMYCETES AND ZYGOMYCETES

Ribosomal RNA molecular weights were determined for 4 species of Smittium (Harpellales, Trichomycetes), Amoebidium parasiticum (Ameobidiales, Trichomycetes), and 16 species in the Mucorales, Kickxellales, and Entomophthorales (Zygomycetes) in an attempt to clarify phylogenetic relationships among these groups of organisms. The ribosomal RNA molecular weights were determined by relative electrophoretic mobility in polyacrylamide gels. The average molecular weights for the heavy (25 S) and light (18 S) ribosomal RNA constituents of the Smittium species were 1.46 × 106 and 0.75 × 106, respectively. The 16 species of fungi in the Mucorales and Kickxellales had distinctly lighter ribosomal RNA molecular weights averaging 1.28 × 106 and 0.70 × 106 for the 25 and 18 S ribosomal RNA constituents, respectively. Molecular weights of Amoebidium parasiticum ribosomal RNAs were 1.36 × 106 and 0.69 × 106. These data suggest that Smittium is not closely related to Amoebidium nor to any of the Mucorales or Kickxellales. © 1979 Academic Press, Inc. All rights reserved.