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Related Concept Videos

Protein Transport to the Stroma01:24

Protein Transport to the Stroma

Chloroplasts are triple membrane structures with an outer membrane, an inner membrane, and a thylakoid membrane, each containing distinct metabolite transporters, membrane translocons, and enzymes. Appropriate sorting and translocating these proteins to their correct membrane systems is essential for chloroplast function.
Protein complexes called the translocon of the outer chloroplast membrane or TOC complex, and the translocon of the inner chloroplast membrane or TIC complex mediate the...
Protein Transport to the Outer Chloroplast Membrane01:11

Protein Transport to the Outer Chloroplast Membrane

Chloroplast outer membrane proteins encoded by the nucleus are synthesized in the cytosol. Soon after synthesis, they bind cytosolic factors such as 14-3-3 protein and the Hsp70 chaperones that keep these precursors in an unfolded state until their translocation.
Two models describe the mechanism of precursor recognition and entry across the outer membrane through the TOC complex. Model 1 suggests the newly synthesized precursor binds to the TOC receptor 159 and forms a complex.
Protein Transport to the Thylakoids01:22

Protein Transport to the Thylakoids

Thylakoids are membrane-bound sac-like structures within the chloroplast that serve as sites for photosynthesis. Thylakoid lumen contains many electron transport proteins and is enclosed by a thylakoid membrane rich in the light-harvesting complex. Proteins targeted to the thylakoids are transported as precursors and are sorted by the general TOC/TIC import pathway. Once the precursor reaches the stroma, stromal processing peptidases remove their transit signal and expose thylakoid signal...
Protein Transport to the Inner Chloroplast Membrane01:18

Protein Transport to the Inner Chloroplast Membrane

Proteins targeted to the inner chloroplast membrane, or plastid proteins, are transported by two general pathways: the stop-transfer and the re-insertion or post-import pathways. Most plastid proteins carry N-terminal transit sequences and internal import sequences targeting it to the specific chloroplast subcompartment. Proteins targeted by the stop-transfer pathway have internal hydrophobic sequences that inhibit their translocation into the stroma. As a result, these precursors are arrested...
Regulation of Expression at Multiple Steps01:23

Regulation of Expression at Multiple Steps

The gene expression in cells is regulated at different stages: (i) transcription, (ii) RNA processing, (iii) RNA localization, and (iv) translation. Transcriptional regulation is mediated by regulatory proteins such as transcription factors, activators, or repressors—these control gene expression by initiating or inhibiting the transcription of genes. Once a precursor or pre-mRNA is produced, it undergoes post-transcriptional modification, including 5' capping, splicing, and the addition of a...
Regulation of Expression Occurs at Multiple Steps02:24

Regulation of Expression Occurs at Multiple Steps

Gene expression can be regulated at almost every step from gene to protein. Transcription is the step that is most commonly regulated. This involves the binding of proteins to short regulatory sequences on the DNA. This association can either promote or inhibit the transcription of a gene associated with the respective sequence.
Transcription results in the generation of precursor (pre-mRNA) that consists of both exons and introns, which needs further processing before being translated to a...

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Related Experiment Video

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Translation Efficiency Test Using Polysome Profiles Under Heat Stress
08:39

Translation Efficiency Test Using Polysome Profiles Under Heat Stress

Published on: October 11, 2024

Chloroplast translation regulation.

Julia Marín-Navarro1, Andrea L Manuell, Joann Wu

  • 1Department of Cell Biology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.

Photosynthesis Research
|July 31, 2007
PubMed
Summary

Chloroplast gene expression hinges on translation regulation, involving unique proteins and RNA elements. Light and assembly processes fine-tune this crucial organelle function.

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Last Updated: Jul 13, 2026

Translation Efficiency Test Using Polysome Profiles Under Heat Stress
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Analysis of Protein Import into Chloroplasts Isolated from Stressed Plants
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Published on: November 1, 2016

Studying Protein Import into Chloroplasts Using Protoplasts
06:29

Studying Protein Import into Chloroplasts Using Protoplasts

Published on: December 10, 2018

Area of Science:

  • Plant Biology
  • Molecular Biology
  • Cell Biology

Background:

  • Chloroplast gene expression is mainly controlled at the translation level of plastid messenger RNAs (mRNAs).
  • Chloroplast translation requires coordination with the nuclear genome and utilizes a translational apparatus with bacterial similarities but unique mechanisms for organelle-specific functions.
  • Plastid ribosomes possess chloroplast-unique proteins and domains that are integral to translational regulation.

Purpose of the Study:

  • To elucidate the regulatory mechanisms governing chloroplast translation.
  • To understand how chloroplast translation responds to environmental cues and internal cellular states.
  • To highlight the role of RNA-protein interactions and subcompartmental localization in controlling gene expression.

Main Methods:

  • Analysis of cis-acting RNA elements in the 5' untranslated region (UTR) of mRNAs.
  • Identification and characterization of trans-acting protein factors involved in translation.
  • Investigation of light-dependent regulatory pathways, including redox state, energy charge (ADP/ATP ratio), and proton gradients.
  • Study of autoinhibition mechanisms in photosynthetic complex assembly.
  • Examination of the role of chloroplast subcompartmentalization in gene expression regulation.

Main Results:

  • Chloroplast translation regulation primarily occurs at the initiation step via RNA-protein interactions.
  • Elongation steps also serve as targets for modulating chloroplast gene expression.
  • Light, redox state, energy levels, and proton gradients significantly influence chloroplast mRNA translation.
  • Assembly of photosynthetic complexes involves autoinhibition of translation to coordinate subunit expression.
  • Subcompartmental localization within chloroplasts is a key regulatory aspect.

Conclusions:

  • Chloroplast translation is a highly regulated process involving intricate RNA-protein interactions and environmental responses.
  • Coordination of gene expression is achieved through multiple layers of control, including initiation, elongation, light signaling, and spatial organization.
  • Understanding these mechanisms is vital for comprehending chloroplast function and adaptation in eukaryotic cells.