The only exception to this is that phage P2 has a 786 bp ORF (orf30) with unknown function inserted between the S and V genes. There is no such insertion in WΦ and L-413C, but Pseudomonas phage ΦCTX (see below) has another uncharacterized ORF located at this position. Enterobacterial phages 186, PSP3, Fels-2, and SopEΦ also share their overall gene order and many genes with P2, but the genes are more diverged. Unlike P2, these phages are UV-inducible

due to the presence of the tum gene. In addition, they have a different lysis-lysogeny switch region. P2 phages seem to have either of two different proteins for repression of the lytic cycle. P2, WΦ and L-413C have the repressor gene C whereas 186, PSP3, Fels-2, SopEΦ, HP1, HP2, and K139 (below) instead have the sequence-unrelated genes CI and CII, both of which are equally needed for establishing lysogeny. Mannheimia phage Φ-MhaA1-PHL101, Pseudomonas learn more phageΦCTX, and Ralstonia phage RSA1 have many P2 genes and an overall order of structural genes that is P2-like, although interspersed with some uncharacterized genes. Their presumed regulatory gene regions include additional putative and uncharacterized ORFs. Phage ΦCTX has only the P2 regulatory gene ogr (transcriptional activator of

the late genes) and the recombination enzyme int (integrase), Φ-MhaA1-PHL101 has repressor (CI) and antirepressor (Cro) equivalents which are most closely related to the regulatory proteins ICG-001 mw of the P22-like enterobacteria phage ST104 than to P2. Phage RSA1 seems to have only one P2-related regulatory gene, the ogr gene, although it is more related to the Ogr/Delta-like gene in ΦCTX. The RSA1 integrase is more similar to the integrases of the P2-like Burkholderia phages (ΦE202, Φ52237, and ΦE12-2 and P22-like viruses. 2. HP1-like viruses The genome architecture of HP1 [36] and its close relative, HP2, resembles that of P2 although

their cos sites, as with Pseudomonas ΦCTX [37], are located next Fenbendazole to attP rather than downstream of the portal protein-encoding gene as it is in P2. The P2 gene order is also conserved in Vibrio phages K139 [38] and κ and the Pasteurella phage F108 [39]. As in P2, the genomes can be divided into blocks of structural and regulatory genes. The structural genes are more similar in HP1 and HP2 than the regulatory genes. The six genes coding for capsid proteins are arranged in the same order in HP1 phages and many P2 phages. The other structural genes, coding mainly for tail components, show generally no similarity to those of P2 phages. Only some of the regulatory genes are similar in both HP1 and P2 phages, e.g., int, CI, and repA. Regulatory genes in general are more conserved within the HP1 group. Aeromonas phage ΦO18P [40] is included into the HP1 phages. It contains slightly more genes related to HP1 than to P2, although, when looking at individual proteins, it sometimes appears to have an intermediate position.