Fig. 4 |. Diversity of skuldviruses.
a, Genome maps of skuldviruses and PM2 virus. Homologous genes are shown using the same colours, with the key provided at the bottom. Also shown is the deduced schematic organization of the skuldvirus virion, with colours matching those of genes encoding the corresponding proteins. Coloured circles indicate the positions of protospacers. Grey shading connects genes displaying sequence similarity at the protein level, with the percentage of sequence identity indicated by different shades of grey (scale on the right). Asterisks denote complete genomes assembled as circular contigs. RCRE, rolling circle replication endonuclease. Genome map of corticovirus PM2 is shown for comparison. b, Sequence similarity network of prokaryotic virus DJR MCPs. Protein sequences were clustered by pairwise sequence similarity using CLANS. Lines connect sequences with CLANS P≤ 1 × 10−4. CLANS uses P values of BLASTP comparisons calculated from Poisson distribution of high-scoring segment pairs. Different previously defined groups42 of DJR MCP are shown as clouds of differentially coloured circles, with the key provided on the right. Note that the Odin group has been named as such previously because some of the MCPs in this cluster originated from Odinarchaeia bin42. The position of Huginnvirus described by Tamarit et al.66 is indicated. Subgroups PRD1, Toil and Bam35 are named after corresponding members of the family Tectiviridae. Skuldviruses are highlighted within a yellow circle. When available, MCP structures of viruses representing each group are shown next to the corresponding cluster (PDB accession numbers given in parentheses). The Skuldvirus cluster is represented by a structural model of the SkuldV1 MCP. Models are coloured according to their secondary structure: α-helices, dark blue; β-strands, light blue.