Replication of Bacterial Viruses

Abstract

The requirement of a DNA/RNA molecule to prime DNA synthesis imposes replication strategies to avoid the lost of the genetic information contained at the 5′-end of the lagging strand. Double-stranded (ds) DNA phages have developed different mechanisms to overcome such a problem. In most cases, phages produce head–tail concatemers, dependent on the presence of terminal redundancies, as in phages T4, T7, and SPP1, or on the circularization and further rolling circle replication, as it occurs in phage λ. Other phages, as ϕ29, have evolved to use a protein to prime DNA synthesis from each end, the priming protein becoming covalently linked to the 5′-ends of the genome. In other cases, as bacteriophage Mu, dsDNA replication depends on its capacity to be integrated into the host genome, replicating as a transposable element, yielding multiple copies of the viral genome at random locations of the bacterial chromosome.

The 5′-replication quandary does not exist in circular single-stranded DNA phages, as ϕX174, which is replicated by a looped rolling circle to produce circular unit length genomes. In the case of ss- and dsRNA phages no such a problem exists since there is specific recognition by the RNA polymerase of the 3′-end of the template RNA.