Figure 1. Discovery of new anti-phage defense systems in defense islands.
(A) Illustration of the computational analysis employed for each pfam found to be enriched in defense islands. Pfams that are enriched in the vicinity of known defense genes are identified, and their neighboring genes are clustered based on sequence homology to identify conserved cassettes that represent putative defense systems. (B) Tendency of protein families to occur next to defense genes. The genomic neighborhood for each member gene in each pfam is examined, and the fraction of member genes occurring in the vicinity (10 genes on each side) of one or more known defense genes is recorded. Pink, a set of 123 pfams known to participate in anti-phage defense (“positive set”); blue, the remaining 13,960 pfams analyzed in this study. (C) Neighborhood variability score for the analyzed pfams. Score represents the fraction of pfam members occurring in different defense neighborhoods out of total occurrences of pfam members (see Methods). Pink, the 123 positive pfams; blue, a set of 576 pfams that passed the 65% threshold for fraction of members occurring with defense genes in proximity.