Differential RNA synthesis in the mitotic cycle of <i>Physarum polycephalum</i>

Nonnucleolar chromatin from interphase nuclei of Physarum polycephalum plasmodia occurs in two different structural configurations as seen in electron microscopic spread preparations. While the majority of the chromatin is devoid of nascent ribonucleoprotein (RNP) fibrils and compacted into nucleosomal particles, a minor proportion (10-20%) is organized differently and reveals a smooth contour. It is this form of smooth chromatin which is rich in transcription units (mean length: 1.36 +/- 0.21 micrometer). Only occasionally are solitary nascent RNP fibrils observed which are associated with beaded strands of chromatin. In transcribed smooth chromatin nucleosomal particles are not only absent from the transcription units but also from their nontranscribed flanking regions, indicating that this special structural aspect is not merely a direct consequence of the transcriptional process. The existence of ca. 10-20% of Physarum chromatin in the smoothly contoured form is discussed in relation to reports of a preferential digestibility of a similar proportion of Physarum chromatin by DNAse I (Jalouzot et al., 1980) and to the altered configuration of "peak A" chromatin subunits after micrococcal nuclease digestion (Johnson et al., 1978 a, b).

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RNA transcription of isolated nuclei and chromatin with exogenous RNA polymerases during mitotic cycle and encystment ofPhysarum polycephalum

Schicker

Hildebrandt

Sauer

1979

Wilhelm Roux' Archiv

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Nuclei have been isolated from plasmodia ofPhysarum. Chromatin has been prepared from these nuclei by lysing them gently with lysolecithin. Both nuclei and chromatin contain endogenous activities of RNA polymerases A and C but not of RNA polymerase B under the conditions specifiied. RNA synthesis of chromatin and nuclei can be stimulated by the addition of purified RNA polymerases. RNA polymerase B is significantly more active than A or the bacterial RNA polymerase fromEscherichia coli. Experiments with specific inhibitors indicate that this additional RNA transcription is due to initiation by exogenously supplied RNA polymerase B. Large RNA products (up to 30 S when analysed under denaturating conditions) are transcribed on chromatin.The template activity of nuclei or chromatin, measured using saturating amounts of added RNA polymerase B, correlates with the in vivo RNA synthesis in three well defined situations. It decreases during starvation when the plasmodium prepares for encystment and is very low during mitosis, however, it is very high during the S-phase of the mitotic cycle when the highest activity of poly(A) + RNA synthesis is detected.

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Differential RNA synthesis in the mitotic cycle of Physarum polycephalum

Cited by 15 publications

References 9 publications

The PhysarumPhysarum Cell Cycle

The PhysarumPhysarum Cell Cycle

Different chromatin structures in Physarum polycephalum

RNA transcription of isolated nuclei and chromatin with exogenous RNA polymerases during mitotic cycle and encystment ofPhysarum polycephalum

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