An efficient method for the extraction of DNA and RNA from fungi is described. Urediosporelings and sporidia of two basidiomycete species and mycellia from several species of Ascomycetes and Oomycetes were homogenized in a lysis buffer containing sodium dodecyl sulfate followed by cetyltrimethylammonium bromide extraction of carbohydrates in 1.4 M NaCl, leaving nucleic acids in the supernatant. After chloroform – isoamyl alcohol extraction of proteins, nucleic acids were precipitated with ethanol. Total nucleic acids prepared in this way contained nuclear, ribosomal, and mitochondrial DNA as well as double-stranded and single-stranded RNA. DNA was eluted from agarose gels and digested with endonucleases, labelled by nick translation, and used for hybridization without nonspecific background signal. A method is also described for RNase digestion of single-stranded and double-stranded RNA in agarose gels. Key words: DNA extraction, double-stranded RNA, cetyltrimethylammonium bromide, sodium dodecyl sulfate.

Uredospores of wheat stem rust (Puccinia graminis Pers. f. sp. tritici Eriks. & E. Henn.) were deposited onto Millipore membranes and allowed to germinate. Those remaining continuously at 20° formed germ tubes only (non-differentiated), but those exposed to 30° for 90 min after the first 2 h of germination developed infection structures corresponding to appressoria and substomatal vesicles (differentiated).Nucleic acids were extracted with a phenol method from resting uredospores and from differentiated and non-differentiated sporelings. The amount of extractable RNA decreased as germination progressed, but no RNA was detected in the germination medium. The decrease in extractable RNA (up to 40%) occurred in both differentiated and non-differentiated sporelings.Acrylamide gel electrophoresis was used to separate RNA species and to determine their approximate molecular weights (in daltons): sporelings contained 25-S (1.65 × 106) and 18-S (0.80 × 106) ribosomal RNA (rRNA), 5-S (3.6 × 104) rRNA, and 4.5-S (2.4 × 104) transfer RNA (tRNA). Radioactive uridine, fed to sporelings, was incorporated mostly into 5-S rRNA and (or) tRNA.Acrylamide gel electrophoresis and sucrose density gradient centrifugation revealed that differentiated sporelings contained a type of RNA that was not detected in non-differentiated sporelings. It was heterogeneous and migrated in the 16-S to 5-S interval on polyacrylamide gels. Some of the RNA present in this fraction may have been preformed in resting spores and released from more complex material during the process of differentiation.