Provirophages and transpovirons as the diverse mobilome of giant viruses.
A distinct class of infectious agents, the virophages that infect giant viruses of the Mimiviridae family, has been recently described. Here we report the simultaneous discovery of a giant virus of Acanthamoeba polyphaga (Lentille virus) that contains an integrated genome of a virophage (Sputnik 2), and a member of a previously unknown class of mobile genetic elements, the transpovirons. The transpovirons are linear DNA elements of ~7 kb that encompass six to eight protein-coding genes, two of which are homologous to virophage genes. Fluorescence in situ hybridization showed that the free form of the transpoviron replicates within the giant virus factory and accumulates in high copy numbers inside giant virus particles, Sputnik 2 particles, and amoeba cytoplasm. Analysis of deep-sequencing data showed that the virophage and the transpoviron can integrate in nearly any place in the chromosome of the giant virus host and that, although less frequently, the transpoviron can also be linked to the virophage chromosome. In addition, integrated fragments of transpoviron DNA were detected in several giant virus and Sputnik genomes. Analysis of 19 Mimivirus strains revealed three distinct transpovirons associated with three subgroups of Mimiviruses. The virophage, the transpoviron, and the previously identified self-splicing introns and inteins constitute the complex, interconnected mobilome of the giant viruses and are likely to substantially contribute to interviral gene transfer.
Aix-Marseille Université, Unité de Recherche sur les Maladies Infectieuses et Tropicales Emergentes, Unité Mixte de Recherche, Centre National de la Recherche Scientifique 7278, Institut de Recherche pour le Développement 198, Institut National de la Santé et de la Recherche Médicale 1095, 13005 Marseille,  France.
Christelle
C
Desnues
Bernard
B
La Scola
Natalya
N
Yutin
Ghislain
G
Fournous
Catherine
C
Robert
Saïd
S
Azza
Priscilla
P
Jardot
Sonia
S
Monteil
Angélique
A
Campocasso
Eugene V
EV
Koonin
Didier
D
Raoult
D001435:Bacteriophages / Q000235:genetics / Q000502:physiology*; D004251:DNA Transposable Elements / Q000502:physiology*; D004279:DNA, Viral / Q000235:genetics; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data
D004251:DNA Transposable Elements; D004279:DNA, Viral