New evolutionary frontiers from unusual virus genomes

Table 1 Characteristics of Mimivirus and CcBV and their genomes

Feature	Mimivirus	CcBV (in caterpillar host)	CcBV (in wasp host)
Genome size (base-pairs)	1,181,404	567,670	NK
Genome structure	Linear	30 closed circles	Provirus (linear)*
G + C composition (%)	28.0	33.95	NK
Coding density (%)	90.5	26.9	NK
Number of genes	1,262	156	NK
Genes containing introns	4^†	107	NK
Genes with assigned function	298	42	NK
Obligate intracellular parasite	Yes	Yes	No^‡
Viral DNA replication in host	Yes	No	No*
Virion assembly in host	Yes	No	Yes
Transmission via virion	Yes	No	No*
Viral gene expression dependent on host cellular machinery	Yes	Yes	Yes

NK, not known; *circles are produced from amplified proviral DNA in female wasps at the time of egg laying, resulting in vertical transmission; ^†genes contain self-splicing introns; ^‡CcBV is not pathogenic to the wasp host and exhibits a mutualistic association with it (see text for details).

ISSN: 1474-760X