DNA structure in the nucleoprotein complex that activates replication of phage phi 29

Bacteriophage-Encoded DNA Polymerases-Beyond the Traditional View of Polymerase Activities

DNA polymerases are enzymes capable of synthesizing DNA. They are involved in replication of genomes of all cellular organisms as well as in processes of DNA repair and genetic recombination. However, DNA polymerases can also be encoded by viruses, including bacteriophages, and such enzymes are involved in viral DNA replication. DNA synthesizing enzymes are grouped in several families according to their structures and functions. Nevertheless, there are examples of bacteriophage-encoded DNA polymerases which are significantly different from other known enzymes capable of catalyzing synthesis of DNA. These differences are both structural and functional, indicating a huge biodiversity of bacteriophages and specific properties of their enzymes which had to evolve under certain conditions, selecting unusual properties of the enzymes which are nonetheless crucial for survival of these viruses, propagating as special kinds of obligatory parasites. In this review, we present a brief overview on DNA polymerases, and then we discuss unusual properties of different bacteriophage-encoded enzymes, such as those able to initiate DNA synthesis using the protein-priming mechanisms or even start this process without any primer, as well as able to incorporate untypical nucleotides. Apart from being extremely interesting examples of biochemical biodiversity, bacteriophage-encoded DNA polymerases can also be useful tools in genetic engineering and biotechnology.

Pleiotropic effect of protein P6 on the viral cycle of bacteriophage phi29

The product of bacteriophage phi29 early gene 6, protein p6, is a double-stranded-DNA binding protein and one of the more abundant proteins during viral infection. We have studied the role of protein p6 in vivo through the infection of suppressor and nonsuppressor Bacillus subtilis strains with a phage carrying a nonsense mutation in gene 6, sus6(626). In the absence of functional protein p6, the two major processes of the viral cycle, transcription and DNA replication, were affected. Viral DNA synthesis was practically abolished, and early transcription was remarkably delayed and, in addition, underregulated at late times of the infection. The amount of protein p6 synthesized after infection with mutant phage sus6(626) under suppressor conditions was sixfold lower than that produced after wild-type infection. Nonetheless, phage production was as high as that obtained after wild-type infection. These results indicate that p6 is synthesized in amounts higher than those needed for most of its functions. However, the concentration of protein p6 appeared to be important for repression of the early promoter C2.