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Journal of Bacteriology, January 2009, p. 135-140, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00778-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Transport of Phage P22 DNA across the Cytoplasmic Membrane{triangledown}

Gerardo L. Perez, Bao Huynh, Miranda Slater, and Stanley Maloy*

Center for Microbial Sciences, Department of Biology, College of Sciences, San Diego State University, San Diego, California

Received 29 June 2008/ Accepted 18 October 2008

Although a great deal is known about the life cycle of bacteriophage P22, the mechanism of phage DNA transport into Salmonella is poorly understood. P22 DNA is initially ejected into the periplasmic space and subsequently transported into the host cytoplasm. Three phage-encoded proteins (gp16, gp20, and gp7) are coejected with the DNA. To test the hypothesis that one or more of these proteins mediate transport of the DNA across the cytoplasmic membrane, we purified gp16, gp20, and gp7 and analyzed their ability to associate with membranes and to facilitate DNA uptake into membrane vesicles in vitro. Membrane association experiments revealed that gp16 partitioned into the membrane fraction, while gp20 and gp7 remained in the soluble fraction. Moreover, the addition of gp16, but not gp7 or gp20, to liposomes preloaded with a fluorescent dye promoted release of the dye. Transport of 32P-labeled DNA into liposomes occurred only in the presence of gp16 and an artificially created membrane potential. Taken together, these results suggest that gp16 partitions into the cytoplasmic membrane and mediates the active transport of P22 DNA across the cytoplasmic membrane of Salmonella.

* Corresponding author. Mailing address: College of Sciences, San Diego State University, 5500 Campanile Dr., San Diego, CA 92182-1010. Phone (619) 594-5142. Fax: (619) 594-6381. E-mail: smaloy{at}sciences.sdsu.edu

{triangledown} Published ahead of print on 31 October 2008.

Journal of Bacteriology, January 2009, p. 135-140, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00778-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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