Figure 1.

Structure of APMV and the core genes and relationship of giant viruses. (A) Viral particles of APMV feature a viral core with the genome, mRNAs, and prefabricated proteins. This core is surrounded by the indicated membranes and the capsid structure that contains a pentagonal, star-shaped structure termed “stargate,” which is involved in the release of the viral core into the host cell's cytosol upon phagocytosis. The capsid is decorated with a compact layer of fibrils. For details see main text. (B) Cladogram displaying the relationships of the different lineages of the Mimiviridae and Marseilleviridae. Since the discovery of APMV, over 100 new mimivirus strains have been characterized using samples of various origins in amoebal co-culture methods (Pagnier et al., 2013; Khalil et al., 2016a,b). All Mimiviridae share a capsid size between 370 and 600 nm and a 1.02–1.26 Mb AT-rich genome which encodes about 1.000 putative proteins (Colson et al., 2017). Based on sequence homology, the Mimiviridae can be divided into three distinct lineages: lineage A with APMV as prototype and a total of 18 members, as reviewed recently (Colson et al., 2017), lineage B with the moumouvirus as prototype and four additional members (Yoosuf et al., 2012; Colson et al., 2017), and lineage C with Megavirus chiliensis as prototype and a total of 12 members (Arslan et al., 2011; Colson et al., 2017). The tree was created using the sequences of the D13 major capsid proteins of the indicated prototype viruses using Phylogeny.fr, with the relative evolutionary distance indicated (Dereeper et al., 2008, 2010). (C) List of nine genes conserved throughout all NCLDV families.