A plant virus movement protein forms ringlike complexes with the major nucleolar protein, fibrillarin, in vitro.
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 ribonucleoprotein 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.
Canetta
Elisabetta
E
BIONTHE (Bio- and Nano-Technologies for Health & Environment) Centre, School of Contemporary Sciences, University of Abertay, Dundee, Bell Street, Dundee DD1 1HG, UK.
Kim
Sang Hyon
SH
Kalinina
Natalia O
NO
Shaw
Jane
J
Adya
Ashok K
AK
Gillespie
Trudi
T
Brown
John W S
JW
Taliansky
Michael
M
D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D018625:Microscopy, Atomic Force; D008854:Microscopy, Electron; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D016366:Open Reading Frames / Q000235:genetics; D053830:Plant Viral Movement Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D020836:Protein Structure, Quaternary
D002868:Chromosomal Proteins, Non-Histone; D009687:Nuclear Proteins; D053830:Plant Viral Movement Proteins; C047458:fibrillarin