PubMed · 6067721
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M L Farr. 1967-04-28. Notes on Myxomycetes.. https://doi.org/10.1007/bf02053430
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We present here direct evidence for the preservation of a transcriptional initiation sequence in a eukaryotic rRNA precursor: the 5'-end group for precursor to 17S rRNA (p17S RNA) from Dictyostelium discoideum is identified as the triphosphate residue pppA-. We also show that mature 5S RNA form Dictyostelium bears a different triphosphate residue, pppG-. In contrast, we find no evidence for more than one phosphate at the 5' end of the 25S rRNA precursor (p25S RNA). These observations indicate that synthesis of the large ribosomal RNAs of Dictyostelium begins with the 5'-terminal sequence of the p17S RNA, and that 5S RNA transcription must be initiated independently, despite the close association of the 5S and rRNA coding segments.
Two basic types of spore wall structures were observed in ultrastructural examination of Schizoplasmodiopsis micropunctata, Schizoplasmodiopsis pseudonendospora, Schizoplasmodipsis reticulata, and Schizoplasmodipsis vulgare. The spores of S. micropunctata, S. pseudoendospora, and S. vulgare had walls bearing electron-dense protrusions, while those of S. reticulata had walls with irregular thickenings. Prominent cytoplasmic features included 2 types of vesicles and electron-dense bodies studded with ribosomes. The ameboid phase of all species lacked the electron-dense bodies and, unlike the dormant phases, did not have mitochondrial surfaces covered with ribosomes.
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