Figure 10-9: Single-gene lysis systems in ssDNA and ssRNA phages. Lysis genes are shaded. Top: Map of MS2, the prototype group I ssRNA phage, with the L sequence displayed above the map. L sequences from the group I phage fr (4), the group II phage GA (62), and the Acinetobacter phage AP205 (70) are arrayed above MS2 L for comparison. Middle: Map of Qbeta, the prototype group III ssRNA phage (106). The regions of close sequence similarity between Qbeta A2 and MS2 A are hatched, and the locations of the por mutations, selected for plaque-formation on a rat host, are indicated by stars (15) (I.-N. Wang and R. Young, unpublished). Bottom: Map of the single-stranded circular DNA phage phiX174, shown linearized at the start of the A gene. The sequence of the E lysis protein is displayed below the map, along with an alignment of the ortholog E proteins from the related phages (top to bottom) G4, alpha3 and S13 (48, 122).