Stored Messenger Ribonucleoprotein Particles in Differentiated Sclerotia of Physarum polycephalum

Adams, David S.; Jeffery, William R.

doi:10.1111/j.1432-0436.1981.tb01174.x

Cited by 12 publications

(5 citation statements)

References 47 publications

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“…The PABPs of birds and mammals range in molecular weight from approximately 70,000 to 80,000 (5,8,24,26,30,46,54,56). The PABP of the yeast Saccharomyces cerevisiae has a molecular weight of 68,000 (1,41), while those of other lower eucaryotes are generally smaller proteins ranging in molecular weight from 18,000 to 60,000 (2,31,33,47). Protein and DNA sequencing of yeast, human, and Xenopus PABPs reveals that these proteins are members of a family of RNA-binding proteins that contain the RNP octapeptide consensus sequence-Lys/Arg Gly Phe/ Tyr Gly/Ala Phe/Tyr Val X Phe/Tyr (1,19,39,59).…”

mentioning

confidence: 99%

Identification and characterization of the poly(A)-binding proteins from the sea urchin: a quantitative analysis.

Drawbridge¹,

Grainger²,

Winkler³

1990

Mol. Cell. Biol.

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confidence: 99%

Identification and characterization of the poly(A)-binding proteins from the sea urchin: a quantitative analysis.

Drawbridge¹,

Grainger²,

Winkler³

1990

Mol. Cell. Biol.

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“…protein complexes [9, 151. The 35 -32s peak present in the pmRNA may constitute a class of mRNPs whose sedimentation behavior resembles that of other lower eucaryotic mRNPs [9]. However, further analyses are needed to identify their components.…”

Section: Discussionmentioning

confidence: 99%

“…These complexes of RNA-protein, known as messenger ribonucleoprotein particles (mRNPs), are found in the nucleus, free in the cytosol (informosomes) or in the polysomal fraction. Free cytoplasmic mRNP has been suggested as being a possible precursor of the polysomal mRNP [8,9]. Indeed, evidence has been presented showing that proteins associated with mRNA in mouse L-cell polyribosomes interchange with free proteins present in the cytosol [lo].…”

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confidence: 99%

Importance of polysomal mRNA‐associated polypeptides for protein synthesis initiation in yeast

Herrera

Triana

Bosch

1988

European Journal of Biochemistry

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The polysomal mRNA from the cell-free system of the yeast Saccharomyces cerevisiae, in the absence of exogenous energy, binds to the 40s ribosomal subunit thus forming a 48s preinitiation complex which, with energy added, is converted into 80s initiation complex. By using ribosomes with a high affinity to polysomal mRNA (pmRNA) from an edeine-resistant mutant of S. cerevisiae in place of wild-type ribosomes, increased quantities of the 48s preinitiation complex are obtained.The pmRNA is found associated with several polypeptides having molecular masses of 11 5 -98 kDa, 72 kDa, 60 kDa and 51 kDa. These polypeptides, labelled with 1251, interact with 40s and 80s ribosomes and are essential for the formation of the 48s and 80s initiation complexes inasmuch as deproteinized pmRNA alone cannot initiate the process. In addition, other polypeptides present in the cytosol are required to carry out the abovementioned steps of protein synthesis.The existence of proteins associated with eucaryotic mRNA has been extensively documented [l -71. These complexes of RNA-protein, known as messenger ribonucleoprotein particles (mRNPs), are found in the nucleus, free in the cytosol (informosomes) or in the polysomal fraction. Free cytoplasmic mRNP has been suggested as being a possible precursor of the polysomal mRNP [8,9]. Indeed, evidence has been presented showing that proteins associated with mRNA in mouse L-cell polyribosomes interchange with free proteins present in the cytosol [lo]. mRNP complexes are composed of several polypeptides that have a wide range of molecular masses. Analyses of the protein composition of cytosol and polysomal mRNP fractions have revealed significant differences in their characteristic protein pattern, although a number of similar major proteins have been observed in both classes of mRNPs [l 1 -161. The presence of common proteins could be responsible for maintaining a defined structural organization of RNP that permits its playing a general role in mRNA metabolism, transportation and translation. The different polypeptides may represent elements of specificity for recruiting or potentiating certain messengers. Recently it has been reported that a 60-kDa messenger ribonucleoprotein exerts a positive control over the translation of mRNA in a cell-free system from embryo axes of dry pea seeds [17]. This type of control mechanism indicates that proteins complexed to polysomal RNP might be one of the keys to protein synthesis initiation.It has also been suggested that structural modifications exist between polypeptides of the cytoplasmic mRNP and polypeptides of the polysomes. This proposal could explain reports of the existence of cytoplasmic mRNPs which are nontranslatable [15, 18 -231. It is possible that specific proteins or modified polypeptides in the cytosol interact with mRNA in such a way that they prevent the entry of mRNA in the translation process: only when these protecting proteins dissociate the complex, may mRNA translation occur. Several reports agree with such an argument [24 -291. Th...

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“…The deficiency in protein synthesis appears to be due to a reduction in the frequency of initiation [Jeffery, 19791. Third, mRNA and ribosomes, which are stored in a functional form by sclerotia [Adams et al, 1981;Halsell and Jeffery, 19861, are gradually driven into polysomes when sclerotia are exposed to low levels of the elongation inhibitor cycloheximide [Jeffery, 19791. The ability to drive mRNA and ribosomes into polysomes permits interactions between the cytoskeleton and translational components to be examined during the suppression of protein synthesis.…”

Section: Discussionmentioning

confidence: 99%

“…As a response to starvation, these plasmodia develop into metabolically dormant sclerotia which are morphologically quite different from plasmodia [Adams et al, 19811 and exhibit reduced levels of protein synthesis [Jeffery, 19791. Although sclerotia contain functional mRNA and ribosomes [Adams et al, 1981;Halsell and Jeffery, 19861, protein synthesis is suppressed at the level of initiation [Jeffery, 19791. In the present investigation, we have tested the possibility that alterations in the cytoskeleton are involved in translational control during the development of sclerotia. The results indicate that protein synthesis does not require an association of polysomes with the cytoskeleton and that the capacity of the cytoskeleton for binding translational components is not altered in sclerotia.…”

Section: Introductionmentioning

confidence: 99%

Translational control and the cytoskeleton in Physarum polycephalum

Brodeur

Jeffery

1987

Cell Motil. Cytoskeleton

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Translationally active plasmodia of the syncytial slime mold Physarum polycephalum develop into translationally dormant sclerotia during starvation. Although functional mRNA and ribosomes exist in sclerotia, protein synthesis is suppressed at the level of initiation. To test the possibility that alterations in the cytoskeleton may limit protein synthesis, we have examined the distribution of polysomes and actin mRNA in the cytoskeletal (CSK) and soluble (SOL) fractions of Triton X-100-extracted plasmodia and sclerotia. Most of the polysomes and actin mRNA were located in the CSK of plasmodia, while most of the ribosomes and actin mRNA were located in the SOL of sclerotia. The results suggest that ribosomes and mRNA shift from the CSK to the SOL as protein synthesis is suppressed during starvation. Plasmodia and sclerotia can be induced to accumulate excess polysomes by treatment with low levels of the elongation inhibitor cycloheximide. Treatment of plasmodia with cycloheximide caused excess polysomes to accumulate in the SOL, suggesting that the CSK contains a limited capacity for binding translational components and that the association of polysomes with the cytoskeleton is not required for protein synthesis. Treatment of sclerotia with cycloheximide, however, caused polysomes and actin mRNA to accumulate in the CSK, suggesting that the sclerotial cytoskeleton, although depleted in ribosomes and mRNA, is capable of binding translational components. It is concluded that alterations in the sclerotial cytoskeleton are not involved in translational control.

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Stored Messenger Ribonucleoprotein Particles in Differentiated Sclerotia of Physarum polycephalum

Cited by 12 publications

References 47 publications

Identification and characterization of the poly(A)-binding proteins from the sea urchin: a quantitative analysis.

Identification and characterization of the poly(A)-binding proteins from the sea urchin: a quantitative analysis.

Importance of polysomal mRNA‐associated polypeptides for protein synthesis initiation in yeast

Translational control and the cytoskeleton in Physarum polycephalum

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