title: 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.
mesh_terms: D001483:Base Sequence; D008970:Molecular Weight; D009698:Nucleoproteins / Q000378:metabolism*; D010804:Physarum / Q000502:physiology*; D011061:Poly A / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000302:isolation & purification / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D009698:Nucleoproteins; D012333:RNA, Messenger; D012261:Ribonucleoproteins; D011061:Poly A; D012313:RNA