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Stored messenger ribonucleoprotein particles in differentiated sclerotia of Physarum polycephalum
Abstract:
Starvation induces vegetative microplasmodia of Physarum polycephalum to differentiate into translationally-dormant sclerotia. The existence and the biochemical nature of stored mRNA in sclerotia is examined in this report. The sclerotia contain about 50% of the poly (A)-containing RNA [poly(A)+RNA] complement of microplasmodia as determined by [3H]-poly(U) hybridization. The sclerotial poly(A)+RNA sequences are associated with proteins in a ribonucleoprotein complex [poly(A)+mRNP] which sediments more slowly than the polysomes. Sclerotial poly(A)+RNP sediments more rapidly than poly(A)+RNP derived from the polysomes of microplasmodia despite the occurrence of poly(A)+RNA molecules of a similar size in both particles suggesting the existence of differences in protein composition. Isolation of poly(A)+RNP by oligo (dT)-cellulose chromatography and the analysis of its associated proteins by polyacrylamide gel electrophoresis show that sclerotial poly(A)+RNP contains at least 14 major polypeptides, 11 of which are different in electrophoretic mobility from the polypeptides found in polysomal poly(A)+RNP. Three of the sclerotial poly(A)+RNP polypeptides are associated with the poly(A) sequence (18, 46, and 52 x 10(3) mol. wt. components), while the remaining eight are presumably bound to non-poly(A) portions of the poly(A)+RNA. Although distinct from polysomal poly(A)+RNP, the sclerotial poly(A)+RNP is similar in sedimentation behavior and protein composition (with two exceptions) to the microplasmodial free cytoplasmic poly(A)+RNP. The results suggest that dormant sclerotia store mRNA sequences in association with a distinct set of proteins and that these proteins are similar to those associated with the free cytoplasmic poly(A)+RNP of vegetative plasmodia.
Insights
Starvation triggers dormant sclerotia formation in Physarum polycephalum, storing messenger RNA (mRNA) with unique proteins. These stored mRNA-protein complexes are similar to those in active cells, suggesting a mechanism for rapid reactivation.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Starvation in Physarum polycephalum induces differentiation into dormant sclerotia.
- Understanding stored genetic material in dormant states is crucial for cell survival and reactivation.
Purpose of the Study:
- To investigate the existence and biochemical nature of stored messenger RNA (mRNA) within Physarum polycephalum sclerotia.
- To characterize the proteins associated with sclerotial mRNA and compare them to those in vegetative microplasmodia.
Main Methods:
- Quantification of poly (A)-containing RNA [poly(A)+RNA] using [3H]-poly(U) hybridization.
- Analysis of ribonucleoprotein complexes [poly(A)+mRNP] via sedimentation and oligo (dT)-cellulose chromatography.
- Protein composition analysis of poly(A)+mRNP using polyacrylamide gel electrophoresis.
Main Results:
- Sclerotia retain approximately 50% of the poly(A)+RNA found in microplasmodia.
- Sclerotial poly(A)+mRNP contains distinct protein components compared to polysomal poly(A)+mRNP from microplasmodia.
- Sclerotial poly(A)+mRNP shares similarities in sedimentation and protein composition with free cytoplasmic poly(A)+mRNP of vegetative microplasmodia.
Conclusions:
- Physarum polycephalum sclerotia store mRNA sequences bound to a specific set of proteins.
- The protein composition of sclerotial mRNA-protein complexes suggests a mechanism for maintaining translational competence during dormancy.
- These findings provide insights into the molecular strategies cells employ to survive adverse conditions and rapidly resume activity.