Mycoplasmal deoxyribonuclease activity in virus-infected L-cell cultures.

Cell-free extracts of Mycoplasma hominis and medium from 72-hr broth cultures had deoxyribonuclease activity like that of deoxyribonuclease I. Mg(++) stimulated activity, and the pH optimum was between 8.0 and 9.0. Double-stranded or heatdenatured deoxyribonucleic acid (DNA) served as a substrate, and oligonucleotides were produced. Cell-free extracts of L cells infected with M. hominis or M. hominis plus equine abortion virus (equine herpes virus, EAV) had greatly increased activity over that of extracts of L cells or of L cells infected with EAV alone. In the absence of M. hominis, however, extracts had little activity, most of which was in virus-infected cell cultures. Activity was found in the culture medium only in those systems in which M. hominis was present. It is concluded that M. hominis can contribute significant deoxyribonuclease activity to virus-infected as well as virusfree cell cultures. Perhaps the most interesting question arising concerns the ability of EAV, a DNA virus, to replicate successfully despite the presence of deoxyribonuclease activity at the site of replication (the nucleus).