Ungerminated conidiospores of Botryodiplodia theobromae were examined for the presence of mRNA. A comparison of the incorporation kinetics of 14C-leucine and 14C-uracil into pulse-labeled germinating spores indicated that a cycloheximide-sensitive protein synthesis began immediately upon germination in the apparent absence of RNA synthesis; the rate of incorporation of 14C-leucine increased sharply later in the germination sequence when an actinomycin D-sensitive 14C-uracil incorporation began. Polyribosomes characteristic of eukaryotic cells were detected in spores at all stages of germination, including the ungerminated spores. The mRNA in polyribosomes of ungerminated spores was probably functional because the ribosomal aggregates became associated in vivo with 14C-labeled amino acids during the first 30 min of germination. Ribosome fractions enriched with polyribosomes were isolated from both ungerminated and germinated spores, and these fractions, when tested with a supernatant enzyme fraction from germinated spores, stimulated appreciably more amino acid incorporation than did purified monoribosomes from the same spores. It is concluded that ungerminated spores of this fungus contain mRNA which is translated immediately upon the onset of germination.
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ACKNOWLEDGMENTS The authors are indebted to Dr. Myron K. Brakke and Mrs. Nancy Van Pelt for generously providing the marker viruses and useful advice about the density-gradient centrifugation. Mr. Don Merlo, Mrs. Sandra Swanda, and Mr. Rex Koski helped provide us with spore material. This investigation was supported in part by funds from the Research Council of the University of Nebraska and from PHS grant Al08057 of the National Xnst.itutes of Health.