Bacteriophage Enzyme Purified From Infected Bacteria Shown to Copy Only Its Own DNA

Towle and colleagues, writing in The Journal of Biological Chemistry in 1975, isolated and characterized an enzyme made by a virus that infects the soil bacterium Pseudomonas putida. This is a study in enzymology and molecular biology, not a medical or skin study: it describes a purified protein and its chemical behavior, not any therapeutic effect.

When the bacteriophage called gh-L infects P. putida, it forces the bacterium to produce a new enzyme, an RNA polymerase, which reads DNA and builds RNA copies of it. The researchers purified this enzyme to near-purity and found it was a single protein chain of about 98,000 molecular weight, distinct from the bacterium's own three-part polymerase. It needed magnesium, not manganese, to work, resisted two common polymerase-blocking drugs (rifampicin and streptolydigin), but was strongly blocked by a related compound called AF/013 and by an ATP look-alike, at concentrations roughly 100 times lower than what was needed to block the host's own enzyme.

Notably, the phage enzyme was choosy about what DNA it would copy: it worked well only on DNA from its own phage, poorly on denatured DNA, and only weakly on synthetic polydeoxyribonucleotides made purely of pyrimidine building blocks. Because this is test-tube biochemistry on bacteria and viruses, it says nothing about effects in animals or humans.