Bacteriophage replicative form

Suitable vectors have been derived from the bacteriophage M13 which, except in its replicating form (RF), contains single-stranded circular DNA. The derivative M13 mpl, produced by insertion of part of the Escherichia coli lac operon, was mutated to give a single site for the restriction endo nuclease EcoRl within the gene for /8-D-galactosidase. This enzyme produces a blue colour when the hosts of this... 

An alternative to repeated cloning of PCR products is a recombination-based approach developed by Liu et al. (1998) to permit the cloning of a PCR product into a plasmid and the rapid conversion of the plasmid to a number of different expression systems without the necessity of cloning the PCR product multiple, independent times. The method, termed the univector plasmid-fusion system (UPS), involves the insertion of the PCR product into a particular type of plasmid, called the univector, which can then be placed under the control of a variety of promoters or fused in-frame to various tag sequences. The system is based upon plasmid fusion using the Cre-lox site-specific recombination system of bacteriophage PI (Sternberg et al., 1981). The Cre enzyme is a site-specific recombinase that catalyzes recombination between two 34 base pair (bp) loxP sequences and is involved in the resolution of dimers formed during replication of the... 

In E. coli cells, DNA replication starts at a specific site called oriC. The oriC locus contains only 245 base pairs. Similar sequences are responsible for initiating the synthesis of plasmid and bacteriophage DNA. The oriC nucleotide sequence binds several units of the tetrameric form of the dnaA protein. This protein is named for the gene that encodes it. The dnaB and dnaC proteins then bind to the complex. As a result of binding these proteins, a portion of the helical DNA is unwound. This forces the rest of the DNA into a left-handed double helix that wraps around the proteins to give a structure... 

Some E. coli bacteriophages, including f2, MS2, R17, and Qj8, as well as some eukaryotic viruses (including influenza and Sindbis viruses, the latter associated with a form of encephalitis) have RNA genomes. The single-stranded RNA chromosomes of these viruses, which also function as mRNAs for the synthesis of viral proteins, are replicated in the host cell by an RNA-dependent RNA polymerase (RNA replicase). All RNA viruses—with the exception of retroviruses—must encode a protein with RNA-dependent RNA polymerase activity because the host cells do not possess this enzyme. 

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