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“Background Bacteriophages of the Leviviridae family are small viruses that infect several genera of Gram-negative bacteria. They have linear, positive-sense, single-stranded RNA genomes about 3500 – 4200 nucleotides in length that encode only four proteins. All Leviviridae phages have three genes in common – maturation, coat and replicase [1]. The replicase cistron encodes the catalytic subunit of the RNA-dependent RNA polymerase complex, which is assembled together with several bacterial

RGFP966 mouse proteins [2, 3] and replicates phage RNA. The coat protein forms dimers, 90 of which assemble in a T=3 icosahedral capsid about 27 nm in diameter and encapsidate the genome [4]. A single copy of the maturation protein binds to phage RNA [5] and gets incorporated into ARN-509 molecular weight capsids along with it. It is required for infectivity of the virions – the maturation protein binds to bacterial pili, then leaves the capsid and enters the cell as an RNA-protein complex [6]. Many of the Leviviridae phages are divided in two genera – leviviruses and alloleviviruses. The major distinction of alloleviviruses is

the presence of a minor coat protein A1 in their capsid which is produced by ribosomal read-through of a leaky termination codon of the coat gene [7]. The other difference is that the maturation protein of alloleviviruses also triggers cell lysis [8, 9], whereas leviviruses encode a dedicated small lysis polypeptide for this purpose [10–12]. The ssRNA phages that infect Escherichia coli cells by adsorbing to F plasmid-coded pili were the first isolates of the Leviviridae family [13, 14], and to date these “male-specific” phages, with type species MS2 and Qβ, have been the most Cisplatin intensively studied and best characterized of this family. However, the F plasmid is just one of the many conjugative plasmids that are present in nature. These plasmids are often highly divergent from F and are most often grouped according to their PXD101 mw mutual compatibility. In Enterobacteriaceae, the conjugative plasmids form more than 20 different incompatibility (Inc) groups which are denoted by capital Latin letters [15]. All these plasmids

encode conjugative pili, but the pilin subunits often share no similarity. Several ssRNA phages specific for conjugative pili other than that of plasmid F have been discovered. Phage PRR1 [16] which adsorbs specifically to IncP plasmid-encoded pili was the first such example, and later other phages specific for Inc group C [17], D [18], H [19, 20], I [21], M [22] and T [23] plasmids followed. Phages PRR1, C-1 (IncC-specific) and Hgal1 (IncH-specific) have been sequenced [24, 25] and phage PRR1 capsids have also been crystallized [26], but no research has been done on the other plasmid-specific phages since their isolation. The IncM plasmid-specific RNA phage M [22] was isolated from sewage in Pretoria, South Africa in the beginning of the 1980s.