The chloroplast 32 kDa protein is synthesized on thylakoid‐bound ribosomes in <i>Chlamydomonas reinhardtii</i>

Herrin, David L.; Michaels, Allan

doi:10.1016/0014-5793(85)80660-8

Cited by 65 publications

(51 citation statements)

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“…2B) either as a ratio (upper plot) or separately (lower plot). All ORFs encoding proteins that were shown previously to integrate cotranslationally into the thylakoid membrane (PsbA, PsbB, PsbC, PsbD, PsaA PsaB, and PetA) (10)(11)(12)(13)22) are represented by prominent membrane-associated peaks, validating the method. Additional peaks revealed the thylakoid-associated translation of 12 proteins that had not been assayed in prior studies: AtpF, AtpI, PetB, NdhA, NdhB, NdhC, NdhD, NdhE, NdhF, NdhG, Ycf4, and CcsA (Fig.…”

Section: Resultsmentioning

confidence: 54%

“…Pioneering studies demonstrated that some chloroplast ribosomes are attached to the thylakoid membrane by the nascent peptide, implying a cotranslational integration mechanism (8,9). Several specific plastid-encoded proteins have been shown to integrate cotranslationally: the PSII subunits PsbA (also known as D1), PsbB, PsbC, and PsbD; the PSI subunits PsaA and PsaB; and the cytochrome b 6 f subunit PetA (also known as cytochrome f) (10)(11)(12)(13)(14). The insertion of PetA into the membrane requires cpSecA (12,15,16), whereas PsbA integrates independent of both the cpSecA and cpTAT systems (17).…”

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confidence: 99%

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Genome-wide analysis of thylakoid-bound ribosomes in maize reveals principles of cotranslational targeting to the thylakoid membrane

Zoschke

Barkan

2015

Proc. Natl. Acad. Sci. U.S.A.

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Chloroplast genomes encode ∼37 proteins that integrate into the thylakoid membrane. The mechanisms that target these proteins to the membrane are largely unexplored. We used ribosome profiling to provide a comprehensive, high-resolution map of ribosome positions on chloroplast mRNAs in separated membrane and soluble fractions in maize seedlings. The results show that translation invariably initiates off the thylakoid membrane and that ribosomes synthesizing a subset of membrane proteins subsequently become attached to the membrane in a nucleaseresistant fashion. The transition from soluble to membraneattached ribosomes occurs shortly after the first transmembrane segment in the nascent peptide has emerged from the ribosome. Membrane proteins whose translation terminates before emergence of a transmembrane segment are translated in the stroma and targeted to the membrane posttranslationally. These results indicate that the first transmembrane segment generally comprises the signal that links ribosomes to thylakoid membranes for cotranslational integration. The sole exception is cytochrome f, whose cleavable N-terminal cpSecA-dependent signal sequence engages the thylakoid membrane cotranslationally. The distinct behavior of ribosomes synthesizing the inner envelope protein CemA indicates that sorting signals for the thylakoid and envelope membranes are distinguished cotranslationally. In addition, the fractionation behavior of ribosomes in polycistronic transcription units encoding both membrane and soluble proteins adds to the evidence that the removal of upstream ORFs by RNA processing is not typically required for the translation of internal genes in polycistronic chloroplast mRNAs.ribosome profiling | protein targeting | plastid | chloroplast | SecA

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Section: Resultsmentioning

confidence: 54%

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confidence: 99%

Genome-wide analysis of thylakoid-bound ribosomes in maize reveals principles of cotranslational targeting to the thylakoid membrane

Zoschke

Barkan

2015

Proc. Natl. Acad. Sci. U.S.A.

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“…4B). These proteins are coded by chloroplast DNA and at least some of them were shown to be synthesized on membranebound ribosomes and inserted co-translationally into the thylakoids (7,9). However, the rate of synthesis on thylakoid-bound ribosomes ( 11) of the smaller one of the two rapidly turned-over 32 kD polypeptides diminished during heat stress by only about 30% in had plants but more (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…However, the rate of synthesis on thylakoid-bound ribosomes (9) of one of the two rapidly turned-over 32 kD polypeptides of PSII is less influenced by heat in had plants but more severely in nad plants. Consequently, continuous formation of 32 kD polypeptide mRNA and its translation at least by a fraction of bound ribosomes proceed at sublethal high temperatures.…”

Section: Discussionmentioning

confidence: 96%

Biosynthetic Cause of in Vivo Acquired Thermotolerance of Photosynthetic Light Reactions and Metabolic Responses of Chloroplasts to Heat Stress

Süss¹,

Yordanov²

1986

Plant Physiol.

108

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Thermotolerance of photosynthetic light reactions in vivo is correlated with a decrease in the ratio of monogalactosyl diacylglycerol to digalactosyl diacylglycerol and an increased incorporation into thylakoid membranes of saturated digalactosyl diacylglycerol species. Although electron transport remains virtually intact in thermotolerant chloroplasts, thylakoid protein phosphorylation is strongly inhibited. The opposite is shown for thermosensitive chloroplasts in vivo. Heat stress causes reversible and irreversible inactivation of chloroplast protein synthesis in heatadapted and nonadapted plants, respectively, but does not greatly affect formation of rapidly turned-over 32 kilodalton proteins of photosystem II. The formation on cytoplasmic ribosomes and import by chloroplasts of thylakoid and stroma proteins remain preserved, although decreased in rate, at supraoptimal temperatures. Thermotolerant chloroplasts accumulate heat shock proteins in the stroma among which 22 kilodalton polypeptides predominate. We suggest that interactions of heat shock proteins with the outer chloroplast envelope membrane might enhance formation of digalactosyl diacylglycerol species. Furthermore, a heatinduced recompartmentalization of the chloroplast matrix that ensures effective transport of ATP from thylakoid membranes towards those sites inside the chloroplast and the cytoplasm where photosynthetically indispensable components and heat shock proteins are being formed is proposed as a metabolic strategy of plant cells to survive and recover from heat stress.Elucidation of the causal sequence of events leading to heat injury and thermotolerance is a key to our understanding of the plant's optimal temperature resistance. There is unequivocal evidence that, prior to the impairment of other cell functions, the photosynthetic apparatus of chloroplasts is irreversibly damaged if the environmental temperature exceeds the upper threshold of the temperature range to which plants are adapted by about 20°C within a few h (reviewed in Berry and Bjorkman [3]). Thermotolerance of photosynthetic processes considerably increases, parallel to the onset of synthesis and accumulation of heat shock proteins (for review see Nover et al. [16]), upon elevation of the temperature to supraoptimal levels (35-45C) (3). At least the heat tolerance of photosynthetic light reactions, which are associated with the chloroplast thylakoid membranes, has been attributed to the heat-induced appearance of polar thylakoid lipids with more saturated fatty acids (3,20). Such changes in the membrane lipid composition are thought to cause an upward shift of the temperature at which an irreversible inactivation of PSII (3) and inhibition of light-activated CO2 fixation (31) occurs.Measurements of the motion of labeled fatty acids have established that the more saturated lipid species considerably decrease the fluidity of thylakoid membranes at high temperatures, thus maintaining an ordered lateral movement of electron carriers between the photosystems, and giv...

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“…The D1 and the D2 proteins are assumed to be inserted into the membrane during their translation on membrane-bound ribosomes [10,11]. It is not clear whether the reaction center chlorophylls bind to these proteins during translation elongation (co-translationally) or after termination of translation (post-translationally).…”

Section: Introductionmentioning

confidence: 99%

Light is required for efficient translation elongation and subsequent integration of the D1‐protein into Photosystem II

Wijk

Eichacker²

1996

FEBS Letters

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The light dependence of translation and successive assembly of the D1 reaction center protein into Photosystem II subcomplexes was followed in fully developed chloroplasts isolated from the dark phase of diurnally grown spinach. The incorporation of synthesized D1 protein into Photosystem II (PSII) was analyzed by fractionation of radiolabeled unassembled protein and PSII (sub)complexes on sucrose density gradients. The ribosomes with attached nascent chains were recovered as pellets in the same gradients, and nascent chains of the D1 protein were immunoprccipitated. The analysis showed that absence of light during translation leads to an increased accumulation of polysome-bound D1 translation intermediates, indicating that light is required for efficient elongation of the D1 protein. The accumulation of the D1 protein and CP43 decreased three-fold in darkness, whereas accumulation of the D2 reaction center protein was not affected by light. In addition, light was also required for efficient incorporation of the D1 protein into the PSII core complex. In darkness, the newly synthesized D1 protein accumulated predominantly as unassembled protein or in PSII subcomplexes smaller than 100 kDa.

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The chloroplast 32 kDa protein is synthesized on thylakoid‐bound ribosomes in Chlamydomonas reinhardtii

Cited by 65 publications

References 23 publications

Genome-wide analysis of thylakoid-bound ribosomes in maize reveals principles of cotranslational targeting to the thylakoid membrane

Genome-wide analysis of thylakoid-bound ribosomes in maize reveals principles of cotranslational targeting to the thylakoid membrane

Biosynthetic Cause of in Vivo Acquired Thermotolerance of Photosynthetic Light Reactions and Metabolic Responses of Chloroplasts to Heat Stress

Light is required for efficient translation elongation and subsequent integration of the D1‐protein into Photosystem II

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