Bacteriophage K1-5 encodes two different tail fiber proteins, allowing it to infect and replicate on both K1 and K5 strains of Escherichia coli - PubMed (original) (raw)

Bacteriophage K1-5 encodes two different tail fiber proteins, allowing it to infect and replicate on both K1 and K5 strains of Escherichia coli

D Scholl et al. J Virol. 2001 Mar.

Abstract

A virulent double-stranded DNA bacteriophage, Phi K1-5, has been isolated and found to be capable of infecting Escherichia coli strains that possess either the K1 or the K5 polysaccharide capsule. Electron micrographs show that the virion consists of a small icosohedral head with short tail spikes, similar to members of the Podoviridae family. DNA sequence analysis of the region encoding the tail fiber protein showed two open reading frames encoding previously characterized hydrolytic phage tail fiber proteins. The first is the K5 lyase protein gene of Phi K5, which allows this phage to specifically infect K5 E. coli strains. A second open reading frame encodes a protein almost identical in amino acid sequence to the N-acetylneuraminidase (endosialidase) protein of Phi K1E, which allows this phage to specifically infect K1 strains of E. coli. We provide experimental evidence that mature phage particles contain both tail fiber proteins, and mutational analysis indicates that each protein can be independently inactivated. A comparison of the tail gene regions of Phi K5, Phi K1E, and Phi K1-5 shows that the genes are arranged in a modular or cassette configuration and suggests that this family of phages can broaden host range by horizontal gene transfer.

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Figures

FIG. 1

FIG. 1

Electron micrograph of ΦK1-5 negatively stained with phosphotungstic acid at a magnification of ×115,500. Morphologically this phage can be classified in the Podoviridae family which includes T7 and SP6.

FIG. 2

FIG. 2

Comparison of the coding regions of the tail proteins of ΦK1-5, ΦK5, and ΦK1E. All three phages share sequence similarity in the upstream region (which contains an SP6 promoter) as well as an 85-base intergenic region. Just downstream of the promoter, ΦK1-5 and ΦK5 encode a lyase protein and ΦK1E encodes ORFL. Immediately following the termination codons of the lyases or ORFL is the intergenic region that contains a potential hairpin structure, the first of which could be a Rho-independent transcription terminator. Immediately following this, ΦK1-5 and ΦK1E encode an endosialidase where ΦK5 encodes ORFP. None of the three phages have any coding regions downstream, and the DNA molecule ends in all three cases. No homology exists in this terminal region.

FIG. 3

FIG. 3

Two possible models for the arrangement of the tails proteins on the phage capsid. (a) There are three copies of each tail forming a hexamer. (b) There are six copies of each tail. One is attached to the head and is part of the core of the tail; the other is then attached to the first tail protein, in effect making a longer tail fiber with two different enzymatic activities.

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