Protein-mediated DNA transfer into liposomes

The transfer of a foreign genome into a bacterium by means of phage infecti on is a very efficient but poorly understood process. To analyse the mechan ism of phage DNA transfer at a molecular level, we have reconstituted FhuA, the receptor for phage T5 in the outer membrane of Escherichia coli, into unilamellar vesicles made of natural phospholipids. Cryoelectron microscopy studies showed that the binding of the phage to FhuA triggered the transfe r of its double-stranded DNA (121 000 bp) into the proteoliposomes. DNA was entrapped within vesicles with a diameter ranging from 70 to 150 nm. The D NA appeared to be densely packed, but its presence did not alter the morpho logy of the liposomes, suggesting no DNA-lipid interactions. These liposome s represent an attractive model system for studying the mechanisms of DNA t ransport and condensation. They may also serve as alternative vehicles for the transfer of foreign genes into eukaryotic cells.