Phage DNA transport across membranes

Phage nucleic acid transport is atypical in bacterial membrane transport: i t is unidirectional and concerns a unique molecule the size of which may re present 50 times that of the bacterium. The rate of DNA transport, although it varies from one phage to another, can reach values as high as 3 000 bp s(-1). This raises the following questions which will be discussed in this review. Is there a single mechanism of transport for all types of phages? D oes the phage genome cross the outer and inner membranes by a unique mechan ism? Is it transported as a free molecule or in association with proteins? How does it avoid periplasmic nucleases? Is such transport dependent on pha ge and/or host cell components? What is the driving force for transport? Re cent cryoelectron microscopy experiments will be presented which show that it is possible to encapsulate a phage genome (121 000 bp) into unilamellar liposomes. The interest of such a model system in gene delivery and in the study of the mechanisms of DNA compaction will be discussed. (C) 1999 Editi ons scientifiques et medicales Elsevier SAS.