C
OMMUNICATION
A Plant Virus Movement Protein Forms Ringlike
Complexes with the Major Nucleolar Protein,
Fibrillarin, In Vitro
Elisabetta Canetta
1
, Sang Hyon Kim
2
, Natalia O. Kalinina
2
, Jane Shaw
2
,
Ashok K. Adya
1
, Trudi Gillespie
2
, John W. S. Brown
2
and Michael Taliansky
2
⁎
1
BIONTHE (Bio- and
Nano-Technologies for Health &
Environment) Centre,
School of Contemporary
Sciences, University of Abertay,
Dundee, Bell Street,
Dundee DD1 1HG, UK
2
Scottish Crop Research
Institute, Invergowrie,
Dundee DD2 5DA, UK
Received 31 October 2007;
received in revised form
17 December 2007;
accepted 18 December 2007
Available online
28 December 2007
Fibrillarin, one of the major proteins of the nucleolus, has methyltransferase
activity directing 2′-O-ribose methylation of rRNA and snRNAs and is
required for rRNA processing. The ability of the plant umbravirus,
groundnut rosette virus, to move long distances through the phloem, the
specialized plant vascular system, has been shown to strictly depend on the
interaction of one of its proteins, the ORF3 protein (protein encoded by open
reading frame 3), with fibrillarin. This interaction is essential for several
stages in the groundnut rosette virus life cycle such as nucleolar import of
the ORF3 protein via Cajal bodies, relocalization of some fibrillarin from the
nucleolus to cytoplasm, and assembly of cytoplasmic umbraviral ribonu-
cleoprotein particles that are themselves required for the long-distance
spread of the virus and systemic infection. Here, using atomic force
microscopy, we determine the architecture of these complexes as single-
layered ringlike structures with a diameter of 18–22 nm and a height of
2.0 ±0.4 nm, which consist of several (n =6–8) distinct protein granules. We
also estimate the molar ratio of fibrillarin to ORF3 protein in the complexes
as approximately 1:1. Based on these data, we propose a model of the
structural organization of fibrillarin–ORF3 protein complexes and discuss
potential mechanistic and functional implications that may also apply to
other viruses.
© 2007 Elsevier Ltd. All rights reserved.
Edited by J. Karn
Keywords: atomic force microscopy; fibrillarin; umbravirus; virus move-
ment; protein complexes
Fibrillarin, one of the major proteins of the
nucleolus, is a core component of box C/D small
nucleolar ribonucleoprotein (RNP) particles and is
required for rRNA processing.
1
Fibrillarin has me-
thyltransferase activity directing 2′-O-ribose methy-
lation of rRNA and snRNAs.
2–4
It is also localized to
another class of subnuclear body or domain, the
Cajal body (CB). CBs are involved in the maturation
of small nuclear RNPs and small nucleolar RNPs,
which traffic through CBs before accumulating in
splicing speckles and the nucleolus, respectively.
5
Although interaction of some animal viruses with
fibrillarin has been reported,
6–9
the specific role of
these interactions in virus life cycles remains largely
uncharacterized.
*Corresponding author. E-mail address:
mtalia@scri.sari.ac.uk.
Present addresses: E. Canetta, Department of Physics,
Faculty of Electronics and Physical Sciences, University of
Surrey, Guildford, Surrey GU2 7XH, UK; S. H. Kim,
Division of Bioscience and Bioinformatics, College of
Natural Science, Myongji University, Yongin 449-728,
South Korea; N. O. Kalinina, A. N. Belozersky Institute of
Physico-Chemical Biology, Moscow State University,
Moscow 119992, Russia.
Abbreviations used: ORF3 protein, protein encoded by
open reading frame 3; RNP, ribonucleoprotein; CB, Cajal
body; GRV, groundnut rosette virus; CP, coat protein;
AFM, atomic force microscopy; EM, electron microscopy;
GAR domain, glycine- and arginine-rich domain.
doi:10.1016/j.jmb.2007.12.039 J. Mol. Biol. (2008) 376, 932–937
Available online at www.sciencedirect.com
0022-2836/$ - see front matter © 2007 Elsevier Ltd. All rights reserved.