The Fate of RNA Degradation Products in Starved Cultures of <i>Tetrahymena pyriformis</i> W.*

Koroly, Mary Jo; Conner, Robert L.

doi:10.1111/j.1550-7408.1974.tb03633.x

Cited by 17 publications

(7 citation statements)

References 44 publications

(9 reference statements)

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“…In no case was enclosure of nucleoli, or other nuclear material, seen as reported by others ( 19); only cytoplasmic components were found in autophagosomes. Starvation of Tetrahymena occurs at the expense of protein (5,19,23), RNA (4,16,17), and phospholipids (13,18) which is in agreement with the observed sequestration of cell organelles, ribosomes, and membrane material. Moreover, the sequential removal of the various cell constituents indicates that autophagy occurs in a well-defined and controlled manner; however, no evidence was found to indicate how material to be sequestred may be selected.…”

Section: Discussionsupporting

confidence: 70%

“…As may be deduced from the table, the number ofautophagosomes increases during the first 3 hours after which the number remains almost constant during prolonged starvation. Since newly formed autophagosomes (Types I, II) decrease in frequency during prolonged starvation, the finding indicates an accumulation of Type IV organeUes which, as mentioned previously (section 3.2), become complex in substructure (Figures 13,16,17).…”

Section: The Occurrence Of Autophagosomes During Starvation and Theirsupporting

confidence: 53%

“…In no instance was nuclear material (nucleoli or chromatin) seen enclosed in autophagosomes. After prolonged starvation, the complexity of the autophagosomal contents increased, thus negative images of apparently dissolved crystals could be seen (Figures 13,16,18). In addition to autophagosomes, the cells contained debris vacuoles, about 3 ~tm in diameter; these became electron dense and complex in structure late during starvation.…”

Section: Autophagosomes and Definition Of Typesmentioning

confidence: 99%

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On starvation-induced autophagy in Teraahymena

Nilsson

1984

Carlsberg Res. Commun.

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Starvation-induced autophagy in Tetrahymena was studied over a 48-hour period during which the cells decreased in size to a quarter of their original volume. The autophagosomes were divided into 4 types: I) Clearly identifiable cytoplasmic content delimited by 2 membranes. II) Clearly identifiable content delimited by one membrane, llI) Content of remnants permitting identification of origin. And, IV) Completely disintegrated content of unknown origin. All types were present in 30-minute starved cells and Type I organdies were seen throughout starvation, thus indicating that autophagy occurred continuously. The number of autophagosomes per unit cytoplasmic area remained constant but with a decrease of the first 3 types and an accumu-lation of Type IV. Acid phosphatase was found in some Type II organelles and in most Types III and IV; these organelles are autolysosomes but Type I is not. Disintegration of the inner autophagosomal membrane (passage from Type I to Type II) thus occurs in the absence oflysosomal enzymes but could be ascribed to an assumed acidification of the organelles. In addition to autophagosomes, profiles were observed of double membrane systems, isolation membranes, enveloping cell constituents as an indication ofautophagy in progress. These isolation membranes seemed to derive from Golgi complexes as tubular, or sac-like structures; moreover, such structures were seen in association with microtubules which indicates a possible transport mechanism to the site ofautophagy. An analysis of the origin of the autophagosomal contents, revealed that cytoplasm was enclosed throughout starvation, whereas enclosure of mitochondria, peroxisomes, and membrane whorls occurred in a time-dependent manner. Hence in this ciliate, autophagy occurs in a well-defined and controlled manner.

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Section: Discussionsupporting

confidence: 70%

Section: The Occurrence Of Autophagosomes During Starvation and Theirsupporting

confidence: 53%

Section: Autophagosomes and Definition Of Typesmentioning

confidence: 99%

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On starvation-induced autophagy in Teraahymena

Nilsson

1984

Carlsberg Res. Commun.

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“…Concomitant with the depreision of ribosome biogenesis, autophagic vacuoles appear in the cytoplasm [50,51]. The cytoplasmic ribosomes appear t o be rapidly degraded as measured hq loss o f K NA from the cells [52], whereas bulk cellulai protein is degraded much inore slowly 1531. Neal-1) 70 ' I ( , ol'the total cellular RNA is degraded in the first hour o f starvation, arrd approximately 30",, is degrrttlect after 3 11 [52,54].…”

Section: Discussionmentioning

confidence: 99%

“…The cytoplasmic ribosomes appear t o be rapidly degraded as measured hq loss o f K NA from the cells [52], whereas bulk cellulai protein is degraded much inore slowly 1531. Neal-1) 70 ' I ( , ol'the total cellular RNA is degraded in the first hour o f starvation, arrd approximately 30",, is degrrttlect after 3 11 [52,54]. After 3 -5 h of starvation the rate o f degradation has decreased to 1 --2'>c11h and remain^ IOU in following period [54].…”

Section: Discussionmentioning

confidence: 99%

Phosphorylation in vivo of Ribosomes in Tetrahymena pyriformis

Kristiansen¹,

Plesner²,

Krüger³

1978

Eur J Biochem

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Phosphorylation of ribosomal proteins in vivo was studied in exponentially growing and starved cells of the ciliated protozoan, Tetrahymena pyriformis. No phosphorylation of ribosomal proteins could be demonstrated in cells growing exponentially in complex nutrient media. However, when Tetrahymenu cells were transferred into a non-nutrient medium, pronounced phosphorylation of a single ribosomal protein was observed. During two-dimensional polyacrylamide gel electrophoresis the phosphorylated ribosomal protein migrated in a manner virtually identical to that of the phosphorylated ribosomal protein S6 of rat liver. The phosphorylated ribosomal protein has a molecular weight of 38 000 as estimated by dodecylsulfate polyacrylamide gel electrophoresis. Thus, the phosphorylated ribosomal protein found in starved Tetrahymena is apparently homologous with the ribosomal protein which is predominantly phosphorylated in higher eukaryotes. When phosphorylated ribosomes were dissociated by treatment with high concentration of KCl, the phosphorylated protein was found only on the small subunit. If dissociation was achieved by dialysis against a buffer low in MgClz, the phosphorylated protein was distributed almost equally between the two subunits. This indicates that the phosphorylated ribosomal protein is located at the interface between the two subunits.Phosphorylation of ribosomal proteins in vivo was initially demonstrated in rabbit reticulocytes [l] and in rat liver [2]. Since then, phosphorylation in vivo has been demonstrated in a number of different tissues from various higher eukaryotes (for review see [3] and [4]). A phosphorylated ribosomal protein was also found in sterile cultures of the higher plant, Lemna minor [5] and recently phosphorylation of several ribosomal proteins in vivo was described for the lower eukaryote, Succharomyces cerevisiae [6,7]. Thus, phosphorylation of ribosomal proteins in vivo seems to be a general phenomenon in eukaryotic cells.Our earlier studies have included cell-cycle-dependent fluctuations in the level of ATP [8] and ribosome biogenesis in the ciliated protozoan, Tetrahymena pyrifovmis [9-111. The pattern of ribosome biogenesis and many structural properties of the ribosomes relate Tetrahymena to higher eukaryotes. Thus, the ribosomes are assembled in the nucleoli in the macronucleus [12,13] and transported into the cytoplasm as nascent ribosomal subparticles containing accessory protein [14]. The sedimentation coefficient of single ribosomes is about 80 S [15,16]. However, the two large ribosomal RNA species are smaller than the corresponding ones in ribosomes from higher eukaryotes and their maturation follows a less complex pathway [17,18]. Furthermore, the ribosomal RNA of Tetrahymenn has a low content of guanine and cytosine [12,18]; this relates it to bacterial ribosomal RNA rather than to eukaryotic ribosomal RNA [19]. EDTA-derived ribosomal subunits from Trtrahymena cosediment with Escherichia coli ribosomal subunits, not with EDTA-derived subunits from Ehrlich ascit...

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Ribosome biosynthesis in Tetrahymena thermophila. III. Regulation of ribosomal RNA degradation in growing and growth arrested cells

Sutton

Hallberg

1979

Journal Cellular Physiology

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We have measured the turnover rate of ribosomal RNA in exponentially growing Tetrahymena thermophila cells, cells entering the plateau phase of growth, and nutrient-deprived (starved) cells. Ribosomal RNA is stable in cells in early log phase growth but it begins to turnover as the cells begin a deceleratory growth phase prior to entering a plateau state. Likewise, rRNA in cells transferred from early log phase growth to a starvation medium begins to be degraded immediately upon starvation. In both cases the degradation of rRNA exhibits biphasic kinetics. A rapid initial exponential degradation with a half time of nine and one-half hours lasting for six hours is followed by a slower exponential degradation with a half-life of 35 hours. When starved cells are transferred to fresh growth medium turnover of rRNA ceases. The evidence presented suggests that the alteration in degradation rate is a regulated process which is most likely independent of the cell cycle.

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The Fate of RNA Degradation Products in Starved Cultures of Tetrahymena pyriformis W.*

Cited by 17 publications

References 44 publications

On starvation-induced autophagy in Teraahymena

On starvation-induced autophagy in Teraahymena

Phosphorylation in vivo of Ribosomes in Tetrahymena pyriformis

Ribosome biosynthesis in Tetrahymena thermophila. III. Regulation of ribosomal RNA degradation in growing and growth arrested cells

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