Intravirion DNA Can Access the Space Occupied by the Bacteriophage P22 Ejection Proteins.

Justin C Leavitt,Carolyn M Teschke,Brianna M Woodbury,Sherwood R Casjens,Eddie B Gilcrease

doi:10.3390/v13081504

Abstract

Tailed double-stranded DNA bacteriophages inject some proteins with their dsDNA during infection. Phage P22 injects about 12, 12, and 30 molecules of the proteins encoded by genes 7, 16 and 20, respectively. After their ejection from the virion, they assemble into a trans-periplasmic conduit through which the DNA passes to enter the cytoplasm. The location of these proteins in the virion before injection is not well understood, although we recently showed they reside near the portal protein barrel in DNA-filled heads. In this report we show that when these proteins are missing from the virion, a longer than normal DNA molecule is encapsidated by the P22 headful DNA packaging machinery. Thus, the ejection proteins occupy positions within the virion that can be occupied by packaged DNA when they are absent.

Highlights

The short-tailed dsDNA bacteriophage P22 virion contains three proteins, the products of genes 7, 16 and 20 that are required for successful delivery of the DNA from the virion into target Salmonella host cells [1,2,3,4,5], but the exact functions of these “ejection proteins” (E-proteins) are not fully understood
All three are quantitatively released from virions during the process of DNA delivery into target cells [2,3,5,6]. After their ejection from the virion these proteins are thought to assemble into a hollow conduit that carries the DNA from the virion through the target cell periplasm into the cytoplasm [7,8,9,10]
In spite of the extensive research on delivery of dsDNA into target cells by tailed phage virions, this process remains poorly understood in detail, and in phage P22 the assembly and function of the E-proteins still present several poorly understood aspects

Summary

Introduction

The short-tailed dsDNA bacteriophage P22 virion contains three proteins, the products of genes 7, 16 and 20 (called gp, gp16 and gp, respectively) that are required for successful delivery of the DNA from the virion into target Salmonella host cells [1,2,3,4,5], but the exact functions of these “ejection proteins” (E-proteins) are not fully understood. All three are quantitatively released from virions during the process of DNA delivery into target cells [2,3,5,6] After their ejection from the virion these proteins are thought to assemble into a hollow conduit that carries the DNA from the virion through the target cell periplasm into the cytoplasm [7,8,9,10]. This idea is strongly supported by the observations that a gp homologue encoded by the Shigella P22-like phage Sf6 assembles in vitro into a hollow tubelike structure with an internal diameter of 25 Å and length of 150 Å [11]. Little is known about the nature of such trans-envelope channels, and we note that the proteins thought to build them in P22, T7 and epsilon are not recognizably related to each other at the sequence level

Methods

Results

Conclusion