Macromolecular events following refeeding of starved

Cameron, Ivan L.; Griffin, Evelyn E.; Rudick, Michael J.

doi:10.1016/0014-4827(71)90001-2

Cited by 23 publications

(3 citation statements)

References 8 publications

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“…This decrease occurs primarily as a result of degradation of ribosomes, because the cell number increases by no more than 5% during this time. This is in contrast to the micronucleate strain HSM which increases 100% during a 24-h starvation (4). This level of ribosomes per cell remains constant for at least 30 h of starvation.…”

Section: Resultsmentioning

confidence: 59%

Nonidentity of ribosomal structural proteins in growing and starved Tetrahymena.

Hallberg¹,

Sutton²

1977

The Journal of Cell Biology

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We have examined the ribosomal structural proteins isolated from vegetatively growing Tetrahymena pyriformis and from cells that had been starved of all nutrients for 24 h. Reproducible, nonartifactual differences in protein complement, primarily associated with the large ribosomal subunit, were found. The kinetics of change in ribosomal protein complement were followed both in refed and in newly starved cells. Furthermore, attempts at correlating a certain protein "phenotype" with a particular functional state of the ribosome were made. It was concluded that the alterations seen could not be correlated with a specific stage in the normal ribosome cycle. We did show, however, that the change in protein complement could occur as a result of altering preexisting ribosomes. In addition, we showed that the change correlates with a decrease in growth rate rather than being caused by the starvation conditions themselves. Speculations as to the functional significance of the protein changes are presented. KEY WORDS ribosomal proteins . nutritional deprivation TetrahyrnenaWe have recently shown (9) that in Tetrahymena pyriformis the ribosome contents of growing cells and nongrowing (starved) cells are regulated at distinct and reproducible levels. Furthermore, the transition from one state (starvation) to the other (exponential growth) involves regulation of ribosome metabolism in a way which indicates that the control of ribosome accumulation in these cells is significantly different than that seen in bacteria. Specifically, we showed that the rate of ribosome synthesis remains constant at a time when the rate of protein synthesis increases some 10-to 15-fold. Also, it appears as if, during this time, ribosomal protein and ribosomal RNA are noncoordinately synthesized. In continuing our studies of ribosome metabolism in T. pyriformis, we have examined further the changes in ribosome number and fraction of active ribosomes in cells shifted either from starvation conditions to growth conditions or vice versa. An unexpected finding of this research is that the proteins of isolated ribosomal subunits from starved and growing cells show reproducible quantitative and qualitative differences when compared by polyacrylamide gel electrophoresis.There have been a number of reports that changes in ribosome structure and/or function can occur in bacteria (e.g., 7, 8, 12) and in eukaryotes (e.g., 6, 10, 15) either during the ribosome cycle or as a response to changes in physiological conditions. We sought to document more carefully the differences we observed, thus hoping we might be able to correlate structural changes with functional ones. We first determined that the differences seen were not the result of an isolation artifact. We than examined the kinetics of change in ribosomal protein "phenotype" when cells were shifted from growth to starvation conditions and

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Section: Resultsmentioning

confidence: 59%

Nonidentity of ribosomal structural proteins in growing and starved Tetrahymena.

Hallberg¹,

Sutton²

1977

The Journal of Cell Biology

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“…The synthesis of ribosomal proteins in the presence of actinomycin D Cameron et al reported that the rate of protein synthesis in Tetrahymenu increased upon refeeding even in the presence of actinomycin D [2]. We, therefore, asked whether the relative rate of r-protein synthesis was also raised upon refeeding in the presence of actinomycin D, in analogy to the increase in r-protein synthesis which was observed in insulin-stimulated chick embryo fibroblasts [13].…”

Section: The Relatiw Rute ?F'synthcsl~ Of'ribosomul Proteins During Amentioning

confidence: 99%

Regulation of ribosome synthesis in Tetrahymena pyriformis. 2. Coordination of synthesis of ribosomal proteins and ribosomal RNA during nutritional shift-up

Dreisig¹,

Andreasen²,

Kristiansen³

1984

Eur J Biochem

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The addition of nutrients to long-time-starved cells of Tetrahymenapyriformis leads to a 50 -60-fold increase in the rate of synthesis of ribosomal proteins (r-proteins). This is achieved by a 6-fold increase in the relative rate of r-protein synthesis and a 8 -10-fold increase in the rate of total protein synthesis. Synthesis of r-proteins constitutes one third of total cellular protein synthesis 2 -4 h after refeeding and the absolute rate of r-protein synthesis is approximately three-times greater than in exponentially growing cells. The synthesis of the individual r-proteins is coordinately regulated during a nutritional shift-up, and de n o w synthesized r-proteins are stable. Addition of actinomycin D prevents the increase in the rate of r-protein synthesis. The rates of synthesis of rRNA and r-protein increase in concert, implying coordinate regulation. Furthermore, a comparison of the observed accumulation of r-proteins with the predicted accumulation based on the accumulation of rRNA suggests that rRNA and r-protein are synthesized in a stoichiometrically balanced way during the entire refeeding period.Addition of nutrients to long-time-starved Tetvahymena cells leads to an ordered sequential reactivation of macromolecular synthesis culminating in the initiation of a rather synchronous cell division about 4 h after refeeding [ 1 -51. An important and integral part of the events leading to the resumption of growth is the restoration of the cellular level of ribosomes [6]. The level of ribosomes in long-time-starved Tetrahymena cells is approximately halved in comparison to exponentially growing cells, and the rate of ribosome production is only about 4.5 % of the rate in exponentially growing cells [6,7]. Following refeeding, the rate of pre-rRNA processing increases rapidly [S]. During the initial period of refeeding the rate of pre-rRNA transcription increases slowly, but around 1.5 h after refeeding, concomitant with the initiation of rDNA replication, the rate of pre-rRNA transcription increases abruptly [8]. From studies using hydroxyurea to inhibit DNA replication, it was suggested that pre-rRNA transcription was gene-dose-dependent [8,9]. By measuring accumulation of total r-protein in mature ribosomes, Hallberg and Bruns estimated that the rate of r-protein synthesis increases about 80-fold during refeeding. Furthermore, it was inferred that r-proteins and rRNA were non-coordinately synthesized during the early period of refeeding [6,10].In this work we examined the rate of synthesis of individual r-proteins during a nutritional shift-up and attempted to measure the stoichiometry of r-protein and rRNA synthesis. We show that the rates of synthesis of individual r-proteins increase coordinately during refeeding. This increase in the rate of synthesis was prevented by the addition of actinomycin D. In addition we show that there is no degradation of de novo synthesized r-protein in refed cells, and finally, we present evidence that, contrary to the suggestion of Hallberg and coworkers [6,10], the s...

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“…Long-time-starved Tetrahymena cells contain a surplus of ribosomes as evidenced by the large pool of inactive 80s ribosomes (Fig. 3), which may in part explain the rapid resumption of protein synthesis after refeeding [1,19,31]. Table 3.…”

Section: The Cellular Content Of R N a And Protein During Nutritionalmentioning

confidence: 99%

Regulation of ribosome synthesis in Tetrahymena pyriformis. 1. Coordination of synthesis of ribosomal proteins and ribosomal RNA during nutritional shift-down

Dreisig¹,

Andreasen²,

Kristiansen³

1984

Eur J Biochem

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When exponentially growing cells of Tetrahymenapyrforrnis are transferred to a non-nutrient medium the loss of whole cell RNA, 90 % of which is ribosomal RNA, exhibits biphasic kinetics, whereas whole cell protein is lost at a constant rate. The ratio RNA/protein declines during the first 5 h of starvation and then remains constant during the subsequent period of starvation. The synthesis of the majority of the ribosomal proteins is coordinately regulated during a nutritional shift-down. Exponentally growing cells devote 17 % of their capacity for protein synthesis to the production of ribosomal proteins. Upon starvation this proportion is rapidly reduced 3.5-fold. In long-time-starved cells the absolute rate of ribosomal protein synthesis is only about 4.5 o/, of that of exponentially growing cells. The synthesis of ribosomal RNA and ribosomal proteins appears tightly coupled during the transition from growth to starvation. In long-time-starved cells the syntheses of ribosomal RNA and ribosomal proteins are stoichiometrically balanced with no significant degradation of de nouo synthesized ribosomal proteins.The potential of members of the genus Tetrahymena for studies on the regulation of ribosome synthesis has been amply demonstrated [I -31. Extraordinarily large variations in the rate of ribosome production occur during a starvationrefeeding cycle of Tetrahymena [I]. In long-time-starved cells less than 3% of the synthesized proteins accumulate in ribosomes, while up to 40% of the newly synthesized proteins can be recovered in ribosomes in refed cells [I]. It was calculated that this represents an 80-fold variation in the rate of accumulation of ribosomal proteins (r-proteins) in ribosomes [I]. The rates of pre-rRNA transcription and processing are severely depressed in starved cells [4,5], but increase rapidly upon refeeding [6]. However, from the data of Hallberg and Bruns [l], it is impossible to tell whether the rate of r-protein synthesis is reduced in concert with the synthesis of rRNA in the starved cells, or whether r-proteins are synthesized in excess of rRNA and then degraded [ 7 ] .In yeast starvation for a required amino acid leads to decrease in the rate of pre-rRNA transcription which is accompanied by a coordinate decrease in the rate of synthesis of most r-proteins [8]. In contrast, inhibition of rRNA transcription during differentiation of L,E, rat myoblasts into myotubes [9] or during a methyl-cellulose-mediated down-shift of mouse 3T3 cells [lo] is not parallelled by a decrease in the relative rate of r-protein synthesis. In fact, evidence was presented indicating that in the case of myoblast differentiation, transcription of r-protein mRNAs persisted unabated for several days. Analogous to other systems, r-proteins synthesized in excess relative to rRNA were rapidly degraded [7,9].The aim of this work was to analyze the synthesis of rproteins in Tetrahymena during a nutritional shift-down, in particular with respect to the coordination of the synthesis of Abbreaiation. r-protein, ribosoma...

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Macromolecular events following refeeding of starved

Cited by 23 publications

References 8 publications

Nonidentity of ribosomal structural proteins in growing and starved Tetrahymena.

Nonidentity of ribosomal structural proteins in growing and starved Tetrahymena.

Regulation of ribosome synthesis in Tetrahymena pyriformis. 2. Coordination of synthesis of ribosomal proteins and ribosomal RNA during nutritional shift-up

Regulation of ribosome synthesis in Tetrahymena pyriformis. 1. Coordination of synthesis of ribosomal proteins and ribosomal RNA during nutritional shift-down

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