Cloning and expression of the ltf gene of bacteriophage T5

Structure of the Receptor-Binding Carboxy-Terminal Domain of the Bacteriophage T5 L-Shaped Tail Fibre with and without Its Intra-Molecular Chaperone

Bacteriophage T5, a Siphovirus belonging to the order Caudovirales, has a flexible, three-fold symmetric tail, to which three L-shaped fibres are attached. These fibres recognize oligo-mannose units on the bacterial cell surface prior to infection and are composed of homotrimers of the pb1 protein. Pb1 has 1396 amino acids, of which the carboxy-terminal 133 residues form a trimeric intra-molecular chaperone that is auto-proteolyzed after correct folding. The structure of a trimer of residues 970–1263 was determined by single anomalous dispersion phasing using incorporated selenomethionine residues and refined at 2.3 Å resolution using crystals grown from native, methionine-containing, protein. The protein inhibits phage infection by competition. The phage-distal receptor-binding domain resembles a bullet, with the walls formed by partially intertwined beta-sheets, conferring stability to the structure. The fold of the domain is novel and the topology unique to the pb1 structure. A site-directed mutant (Ser1264 to Ala), in which auto-proteolysis is impeded, was also produced, crystallized and its 2.5 Å structure solved by molecular replacement. The additional chaperone domain (residues 1263–1396) consists of a central trimeric alpha-helical coiled-coil flanked by a mixed alpha-beta domain. Three long beta-hairpin tentacles, one from each chaperone monomer, extend into long curved grooves of the bullet-shaped domain. The chaperone-containing mutant did not inhibit infection by competition.

Crystallization of the C-terminal domain of the bacteriophage T5 L-shaped fibre

Tails of bacteriophage T5 (a member of the Siphoviridae family) were studied by electron microscopy. For the distal parts of the L-shaped tail fibres, which are involved in host cell receptor binding, a low-resolution volume was calculated. Several C-terminal fragments of the fibre were expressed and purified. Crystals of two of them were obtained that belonged to space groups P63 and R32 and diffracted synchrotron radiation to 2.3 and 2.9 Å resolution, respectively. A single-wavelength anomalous dispersion data set to 2.5 Å resolution was also collected from a selenomethionine-derivatized crystal of one of the fragments, which belonged to space group C2.

Complete genome sequence of bacteriophage T5

The 121,752-bp genome sequence of bacteriophage T5 was determined; the linear, double-stranded DNA is nicked in one of the strands and has large direct terminal repeats of 10,139 bp (8.3%) at both ends. The genome structure is consistently arranged according to its lytic life cycle. Of the 168 potential open reading frames (ORFs), 61 were annotated; these annotated ORFs are mainly enzymes involved in phage DNA replication, repair, and nucleotide metabolism. At least five endonucleases that believed to help inducing nicks in T5 genomic DNA, and a DNA ligase gene was found to be split into two separate ORFs. Analysis of T5 early promoters suggests a probable motif AAA{3, 4 T}nTTGCTT{17, 18 n}TATAATA{12, 13 W}{10 R} for strong promoters that may strengthen the step modification of host RNA polymerase, and thus control transcription of phage DNA. The distinct protein domain profile and a mosaic genome structure suggest an origin from the common genetic pool.

Proteolytic processing and oligomerization of bacteriophage-derived endosialidases

Bacteriophages infecting the neuroinvasive pathogen Escherichia coli K1 require an endosialidase to penetrate the polysialic acid capsule of the host. Sequence information is available for the endosialidases endoNE, endoNF, and endoN63D of the K1-specific phages phi K1E, phi K1F, and 63D, respectively. The cloned sequences share a highly conserved catalytic domain but differ in the length of the N- and C-terminal parts. Although the expression of active recombinant enzyme succeeded in the case of endoNE, it failed for endoNF. Protein alignments of all three endosialidase sequences gave rise to the assumption that inactivity of the cloned endoNF is caused by a C-terminal truncation. By reinvestigation of the respective gene locus in the phi K1F genome, we identified an extended open reading frame of 3195 bp, encoding a 119-kDa protein. Full-length endoNF contains the C-terminal domain conserved in all endosialidases, which may act as an intramolecular chaperone. Comparative studies carried out with endoNE and endoNF demonstrate that endosialidases are proteolytically processed, releasing the C-terminal domain. Using a mutational approach in combination with protein analytical techniques we demonstrate that (i) the C-terminal domain is a common feature of endosialidases and other tail fiber proteins; (ii) the integrity of the C-terminal domain and its presence in the nascent protein are crucial for the formation of active enzymes; (iii) proteolytic processing is not essential for enzymatic activity; and (iv) functional folding is a prerequisite for trimerization of endoNF.

The nucleotide sequence of the bacteriophage T5 ltf gene

The nucleotide sequence of the bacteriophage T5 Bg/II-BamHI fragment (4,835 bp in length) known to carry a gene encoding the LTF protein which forms the phage L-shaped tail fibers was determined. It was shown to contain an open reading frame for 1,396 amino acid residues that corresponds to a protein of 147.8 kDa. The coding region of ltf gene is preceded by a typical Shine-Dalgarno sequence. Downstream from the ltf gene there is a strong transcription terminator. Data bank analysis of the LTF protein sequence reveals 55.1% identity to the hypothetical protein ORF 401 of bacteriophage lambda in a segment of 118 amino acids overlap.

Cloning, sequencing, and recombinational analysis with bacteriophage BF23 of the bacteriophage T5 oad gene encoding the receptor-binding protein

Binding of bacteriophage T5 to its receptor, the Escherichia coli FhuA protein, is mediated by tail protein pb5. In this article we confirm that pb5 is encoded by the T5 oad gene and describe the isolation, expression, and sequencing of this gene. In order to locate oad precisely, we analyzed recombinants between BF23, a T5-related phage with a different host range, and plasmid clones containing segments of the T5 chromosome. This analysis also showed that oad has little or no homology with hrs, the analogous BF23 gene. We were able to overproduce a protein that comigrates with pb5 after fusing a 2-kb segment containing oad to a phage T7 promoter. This segment contains an open reading frame that can encode a protein of the appropriate size. Its deduced amino acid sequence does not closely resemble that of any other protein in the database. The sequence upstream of the open reading frame shows typical characteristics of a promoter region with two overlapping, divergently orientated promoters.

Characterization and expression of a cloned tetracycline resistance determinant from Campylobacter jejuni plasmid pUA466

A tetracycline resistance (Tcr) determinant previously cloned from the Campylobacter jejuni plasmid pUA466 (D. E. Taylor, J. Bacteriol. 165:1037-1039, 1986) was localized by restriction endonuclease mapping, subcloning, and Tn1000 insertion mutagenesis to a 2-kilobase region consisting of 1.8- and 0.2-kilobase HincII fragments. Tcr encoded by the cloned fragment (pUOA1) was expressed constitutively in Escherichia coli. A protein with an apparent molecular weight of 68,000 encoded by pUOA1 was produced in an in vitro transcription-translation system and in minicells. Tn1000 insertions which resulted in inactivation of Tcr expression also resulted in an alteration in the 68,000-molecular-weight protein. Some mutants specified a truncated protein, whereas others completely lost the ability to specify the protein. The protein which appears to be involved in the expression of Tcr specified by C. jejuni plasmids is of approximately the same molecular weight as the protein specified by the streptococcal class M determinant. This finding is consistent with our previous results which indicate that homology exists between the Tcr determinant from C. jejuni and a 5-kilobase HincII probe derived from the streptococcal class M determinant.

Location of genes D16, D17, and N4 encoding tail proteins on the physical map of bacteriophage T5

Bacteriophage T5 DNA fragments were cloned into plasmid pBR322. Recombinant plasmids complementing T5 amber mutants were isolated, and used as hybridization probes with T5 DNA in Southern blots. Employing this approach the three T5 genes D16, D17, and N4 were mapped with respect to the physical map of T5, and shown to be located at 74%, 72%, and 82% of the genome, respectively.