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Journal of Bacteriology, August 2005, p. 5397-5405, Vol. 187, No. 15
0021-9193/05/$08.00+0     doi:10.1128/JB.187.15.5397-5405.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

The Holin Protein of Bacteriophage PRD1 Forms a Pore for Small-Molecule and Endolysin Translocation

Gabija iedait,^1,2 Rimantas Daugelaviius,^1,2 Jaana K. H. Bamford,¹ and Dennis H. Bamford^1*

Department of Biological and Environmental Sciences and Institute of Biotechnology, Biocenter 2, P.O. Box 56 (Viikinkaari 5), 00014 University of Helsinki, Finland,¹ Department of Biochemistry and Biophysics, Vilnius University, iurlionio 21, 03101 Vilnius, Lithuania²

Received 6 December 2004/ Accepted 27 April 2005

PRD1 is a bacteriophage with an icosahedral outer protein layer surrounding the viral membrane, which encloses the linear double-stranded DNA genome. PRD1 infects gram-negative cells harboring a conjugative IncP plasmid. Here we studied the lytic functions of PRD1. Using infected cells and plasmid-borne lysis genes, we demonstrated that a two-component lysis system (holin-endolysin) operates to release progeny phage particles from the host cell. Monitoring of ion fluxes and the ATP content of the infected cells allowed us to build a model of the sequence of lysis-related physiological changes. A decrease in the intracellular level of ATP is the earliest indicator of cell lysis, followed by the leakage of K⁺ from the cytosol approximately 20 min prior to the decrease in culture turbidity. However, the K⁺ efflux does not immediately lead to the depolarization of the cytoplasmic membrane or leakage of the intracellular ATP. These effects are observed only 5 to 10 min prior to cell lysis. Similar results were obtained using cells expressing the holin and endolysin genes from plasmids.

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