Figure 1

Gene arrangement of prototypical ICE Hptfs3 (A) and ICE Hptfs4 (B) islands. Genes encoding type IV secretion system components are drawn as red arrows, and other genes as grey arrows. Regions with high nucleotide sequence similarity are connected by dark grey bars, and regions with low to intermediate levels of similarity by light grey bars. Hatched arrows indicate orthologous, but clearly distinct gene variants. Typical sizes of the corresponding elements are indicated on the left. ICEHptfs3 elements differ by the presence or absence of pz21-pz23 genes (according to the nomenclature of [15]) and by several distinct variants of the pz34, pz35, and/or pz36 genes. However, variations within these two regions do not correlate with each other and were thus not considered for ICEHptfs3 subclassification. In contrast, ICEHptfs4 islands are further subclassified into ICEHptfs4a, ICEHptfs4b and ICEHptfs4c groups according to the presence of orthologous gene variants. Note that the polymorphic genes hpp12_446/hpg27_981 and hpp12_444-445/hpg27_982 could not clearly be assigned to ICEHptfs4a or ICEHptfs4b and were thus not considered for classification of ICEHptfs4 subtypes. LJ, left junction; RJ, right junction.