Bacteriophages with ssRNA

The single-stranded ribonucleic acid (ssRNA) phages are small icosahedral viruses which infect their host via F- or polar pili. The best-characterised are those infecting Escherichia coli, a Gram-negative bacterium found in the gut and faecal sewage. The ssRNA phages are members of the Leviviridae family, which includes the two genera Levivirus and Allolevivirus. The family presently comprises about 100 isolates including the well-known MS2 and Qβ coliphages.Their genome size ranges from 3400 to 4300 nt and codes for four proteins. The genome of ssRNA phages adopts a unique structure that regulates translation of the four genes, confers RNase resistance in the bacterial cytoplasm, ensures recognition by replicase and facilitates encapsidation by capsid or coat proteins. The interaction between RNA and coat protein by virtue of its high specificity and strength is used in many molecular biological applications. Key Concepts: ssRNA phages are members of the Leviviridae family which comprises the genera Levivirus and Allolevivirus. ssRNA phages infect their hosts via pili. The nonenveloped quasi-icosahedral shell of the virion has a T=3 surface lattice. RNA inside the virion is structured. The genome encodes four types of proteins: maturation, coat, lysis and replicase. Replication requires the use of host proteins. Translation of the genes is regulated by RNA secondary structure. Forced evolution experiments reveal constraints on RNA secondary structure. Phage particles can be used to display foreign epitopes. RNA phages are used as indicator organisms for the presence of pathogens in drink and surface water. Keywords: RNA; phage; translation; replication; evolution; RNA recombination; RNA secondary structure; index organism; sewage; ribosome; fitness