DNA translocation across planar bilayers containing Bacillus subtilis ion channels

Abstract

The mechanisms by which genetic material crosses prokaryotic membranes are incompletely understood. We have developed a new methodology to study the translocation of genetic material via pores in a reconstituted system, using techniques from electrophysiology and molecular biology. We report here that planar bilayer membranes become permeable to double-stranded DNA (kilobase range) if Bacillus subtilis membrane vesicles containing high conductance channels have been fused into them. The translocation is an electrophoretic process, since it does not occur if a transmembrane electrical field opposing the movement of DNA, a polyanion, is applied. It is not an aspecific permeation through the phospholipid bilayer, since it does not take place if no proteins have been incorporated into the membrane. The transport is also not due simply to the presence of polypeptides in the membrane, since it does not occur if the latter contains gramicidin A or a eukaryotic, multi-protein vesicle fraction exhibiting 30-picosiemens anion-selective channel activity. The presence of DNA alters the behavior of the bacterial channels, indicating that it interacts with the pores and may travel through their lumen. These results support the idea that DNA translocation may take place through proteic pores and suggest that some of the high conductance bacterial channels observed in electrophysiological experiments may be constituents of the DNA translocating machinery in these organisms.