In addition to the above analysis, ten syntactic models were developed using proteins conserved in the three sequenced ascovirus species (SfAV1a, TnAV2c, and HvAV3a) and twelve iridoviruses [36] . None of these 1 and 4, typed in black) , DpAV4 (lanes 2 and 5, typed in blue) and SfAV1a (lanes 3 and 6, typed in purple) . Conserved positions among the amino acid sequence of CsIV and those of DpAV4 and SfAV1a are highlighted in grey. Secondary structures in the three SfAV1a ORF061 orthologs were calculated with the Network Protein Sequence Analysis at http://npsa-pbil.ibcp.fr/ and the statistical relevance of the secondary structures were evaluated with Psipred at http://bioinf.cs.ucl.ac.uk/psipred/. C, E and H in lanes 4 to 6 respectively indicated for each amino acid that it is involved in a coiled, b sheet or a helix structure. Using default parameters of Psipred, upper case letters indicate that the predicted secondary structure is statically significant in Psipred results. Significant secondary structures are highlighted in yellow. In (a), the comparisons were limited to three of the seven conserved domains (Additional file 3a, b and 3c), the 2, 5 and 7. Indeed, classical in silico methods appeared to be inappropriate to predict statistically significant secondary structures in conserved structural protein rich in b strand such as iridovirus and ascovirus MCP. In contrast, a complete and coherent domain comparison was obtained by HCA profiles (fig. S3b, c) . , developed from small proteins encoded by the DpAV4 ORF041, SfAV1a ORF061, HvAV3a ORF74, and TnAV2c ORF118 in the ascovirus genomes, and iridovirus CIV ORF347L and mimivirus MIV ORF096R genomes, respectively. Importantly, these proteins have orthologs in vertebrate iridoviruses, phycodnaviruses, and asfarvirus. In SfAV1a, the peptide encoded by ORF061 is one of the virion components. In ascoviruses, iridoviruses, phycodnaviruses, and the asfarvirus, they have been annotated as thioredoxines, proteins that play a role in initiating viral infection [37] [38] [39] . Database mining with our model revealed four hits with CsIV sequences (Acc N°. M80623, S47226, AF236017, AF362508) each a homolog ORF of SfAV1a ORF061. In fact, these sequences correspond to several variants of a single region contained in the B segment of the CsIV genome. To date, these have not been annotated in the final CsIV genome, probably because they overlap a recombination site. HCA analyses confirmed that the hydrophobic cores were conserved ( Fig. 3b and Additional file 3d and 3e).