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SUMMARY:Protein import into chloroplasts and its regulation by the ubiquit
 in-proteasome system - R. Paul Jarvis\, Section of Molecular Plant Biology
 \, Department of Biology\, University of Oxford 
DTSTART:20221013T111500Z
DTEND:20221013T124500Z
UID:TALK182894@talks.cam.ac.uk
CONTACT:Jake Harris
DESCRIPTION:The development and operation of plant chloroplasts (or plasti
 ds) requires the participation of thousands of organellar proteins. Most c
 hloroplast proteins are nucleus-encoded and synthesized in the cytosol in 
 precursor form. These preproteins pass through multiprotein import machine
 s in the organelle’s outer and inner envelope membranes\, called the TOC
  and TIC translocons. Receptors components of the TOC complex exist in mul
 tiple isoforms\, and genetic studies in the model plant Arabidopsis have i
 ndicated that the isoforms have distinct preprotein recognition specificit
 ies and function in different import pathways. Operation of such client-sp
 ecific import pathways controls the organelle’s proteome and functions\,
  and plays a role in the differentiation of different plastid types (e.g.\
 , the chromoplasts formed in ripening tomato fruit). Our work has shown th
 at the chloroplast protein import machinery is proteolytically regulated b
 y direct action of the ubiquitin-proteasome system (UPS)\, in a process te
 rmed “chloroplast-associated protein degradation” (CHLORAD). The CHLOR
 AD machinery has three key components: the SP1 ubiquitin E3 ligase\, the S
 P2 β-barrel channel protein\, and the CDC48 AAA+ ATPase. The SP1 and SP2 
 proteins form a complex in the outer envelope membrane\, and respectively 
 mediate the ubiquitination and extraction (or retrotranslocation) of TOC p
 rotein targets. The CDC48 protein\, located in the cytosol\, provides the 
 energy that drives the retrotranslocation step\, delivering the target pro
 teins to the cytosolic 26S proteasome for degradation. Recent advances in 
 our understanding of the mechanisms and functions of CHLORAD will be discu
 ssed.\n\n
LOCATION:Large Lecture Theatre\, Department of Plant Sciences\,
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