Nuclease content of group H Streptococcus strain Challis cell surface extracts inactivating transforming deoxyribonucleic acid.

Besides the competence factor (cpf), the activity of nuclease present in cell surface extracts (iF) is most likely necessary for the occurrence of competence in transformation of Challis strain and other group H streptococci. Very small amounts of iF activity were available. For this reason there were no data on nucleases occurring in iF preparations. In our previous studies, three deoxyribonucleases (endonucleases) were isolated and partly purified from stationary Challis strain cells. In the present work, due to the application of stationary-phase cell endonucleases, gel electrophoresis, and the immunological method, we found that two of these nucleases occur in Challis strain iF preparations. These two nucleases are present in larger amounts at the cell surface only in cells originating from the early-logarithmic-phase culture. Only in this phase does competence occur in the Challis strain. Antibodies against the three endonucleases of the Challis strain do not block the occurrence of competence. We suggest that an increase in the permeability of the cell membrane for intracellular nucleases independent of cpf activity is a stage in the maturation of competence.