Histone Proteins Found to Control DNA-Copying Enzyme in Leukemia Virus

Manly and colleagues, writing in the Journal of Virology in 1974, examined how histones — proteins that DNA normally wraps around in cells — affect an enzyme from the Moloney murine leukemia virus that copies RNA into DNA. This is a laboratory biochemistry study, not one involving animals or people; it used virus particles broken open with detergent, mixed with synthetic RNA templates such as polyadenylate, polycytidylate, and polyuridylate.

The researchers found that histones could either speed up or slow down the enzyme's DNA-building activity, depending on how much histone was present relative to the RNA template. One histone fraction, called f1, produced both the strongest boost and the strongest block. The same histone had the opposite effect on a bacterial DNA-copying enzyme from Micrococcus luteus, which was slowed by histone amounts that sped up the viral enzyme. The best histone concentration scaled with the amount of RNA template present, suggesting histone binds directly and proportionally to the template rather than to the enzyme or virus itself.

The authors suggest a histone-like protein might play a role when these RNA viruses build their DNA copy inside cells, but the study only shows this in a test tube system and cannot demonstrate what happens inside a living cell or organism.