Enchancement of streptococcal transformation yield by proteolytic enzymes

Trypsin and other proteolytic enzymes, added together with transforming DNA or during cell-DNA contact to competent cultures of several streptococcal strains, enchanced (10 to 600%) the yield of genetic transformation (stimulation). With few exceptions, the level of stimulation was high (over 100%) when competence was low (below 2%). Stimulation was caused by the action of an enzyme on competent cells and not on any other component of transformation mixture. The phenomenon occurred when the enzyme was added to the culture not earlier than 7 min before and not later than 5 min after the period of cell-DNA contact. The presence of trypsin during cell-DNA contact caused: (i) the alterations at cell surface, demonstrated by electron microscopy, increased release of 3H-amino acid-labeled material, and higher cell susceptibility to autolysis; (ii) the increase of both total and irreversible binding of DNA by the cells; and (iii) the decrease of early nucleolytic degradation of DNA by cells. These and other data point to the importance of a delicate balance of recipient cell's surface nuclease activities in the effectiveness of transformation process. It is also possible that trypsin eliminates an unknown cellular factor which obstructs DNA-cell receptors interaction.