Review
Translocation of proteins across the multiple membranes of
complex plastids
Giel G. van Dooren
a
, Steven D. Schwartzbach
b
, Tetsuaki Osafune
c
,
Geo¡rey I. McFadden
aY
*
a
Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Melbourne, Vic. 3010, Australia
b
Department of Microbiology and Molecular Cell Sciences, University of Memphis, Memphis, TN 38152, USA
c
Department of Life Sciences, Nippon Sport Science University, Yokohama 227, Japan
Received 13 August 2001; accepted 13 August 2001
Abstract
Secondary endosymbiosis describes the origin of plastids in several major algal groups such as dinoflagellates, euglenoids,
heterokonts, haptophytes, cryptomonads, chlorarachniophytes and parasites such as apicomplexa. An integral part of
secondary endosymbiosis has been the transfer of genes for plastid proteins from the endosymbiont to the host nucleus.
Targeting of the encoded proteins back to the plastid from their new site of synthesis in the host involves targeting across the
multiple membranes surrounding these complex plastids. Although this process shows many overall similarities in the
different algal groups, it is emerging that differences exist in the mechanisms adopted. ß 2001 Published by Elsevier
Science B.V.
Keywords: Malaria; Protein transport; Endoplasmic reticulum; Vesicle; Golgi apparatus
1. Introduction
Imagine you are in a boat, on the ocean, about 600
million years ago. In the water around you an entire
biosystem £ourishes, with red and green algae at the
base of a food web that provides nutrients for inver-
tebrates like trilobites and top-of-the-foodchain pred-
ators like Anomalocarus. The importance of algae in
these biosystems is due to their ability to obtain en-
ergy from the sun and convert this to sugar. The
ability of these eukaryotic (nucleated) organisms to
photosynthesize was acquired hundreds of millions
years earlier [1], through a process called primary
endosymbiosis.
Primary endosymbiosis arose when a non-photo-
synthetic eukaryote acquired the services of a photo-
synthetic cyanobacterium (Fig. 1). Current evidence,
based largely on phylogenetic trees of algal proteins
and preservation of operons, suggests that primary
endosymbiosis was a singular event [2^4], with this
primordial photosynthetic eukaryote diverging into
the red algal and green algal/plant lineages. If,
when standing in your boat 600 or so million years
ago (the actual dates are not clear), you had a plank-
ton ¢lter and a decent enough microscope, you might
witness the beginnings of a second wave of algal
evolution. This wave, known as secondary endosym-
0167-4889 / 01 / $ ^ see front matter ß 2001 Published by Elsevier Science B.V.
PII: S0167-4889(01)00154-9
* Corresponding author.
E-mail address: g.mcfadden@botany.unimelb.edu.au
(G.I. McFadden).
BBAMCR 14807 11-12-01
Cyaan Magenta Geel Zwart
Biochimica et Biophysica Acta 1541 (2001) 34^53
www.bba-direct.com