The Deoxyribonuclease Induced after Infection of Escherichia coli by Bacteriophage T5

Characterization and genome analysis of Escherichia phage fBC-Eco01, isolated from wastewater in Tunisia

The rise of antibiotic resistance in bacterial strains has led to vigorous exploration for alternative treatments. To this end, phage therapy has been revisited, and it is gaining increasing attention, as it may represent an efficient alternative for treating multiresistant pathogenic bacteria. Phage therapy is considered safe, and phages do not infect eukaryotic cells. There have been many studies investigating phage-host bacteria interactions and the ability of phages to target specific hosts. Escherichia coli is the causative agent of a multitude of infections, ranging from urinary tract infections to sepsis, with growing antibiotic resistance. In this study, we characterized the Escherichia phage fBC-Eco01, which was isolated from a water sample collected at Oued, Tunis. Electron microscopy showed that fBC-Eco01 phage particles have siphovirus morphology, with an icosahedral head of 61 ± 3 nm in diameter and a non-contractile tail of 94 ± 2 nm in length and 12 ± 0.9 nm in width. The genome of fBC-Eco01 is a linear double-stranded DNA of 43.466 bp with a GC content of 50.4%. Comparison to databases allowed annotation of the functions to 39 of the 78 predicted gene products. A single-step growth curve revealed that fBC-Eco01 has a latent period of 30 minutes and a burst size of 175 plaque-forming units (PFU) per infected cell. Genomic analysis indicated that fBC-Eco01 is a member of the subfamily Guernseyvirinae. It is most closely related to a group of phages of the genus Kagunavirus that infect Enterobacter, Raoultella, and Escherichia strains.

It seems like only yesterday

I spent my childhood and adolescence in North and South Carolina, attended Duke University, and then entered Duke Medical School. One year in the laboratory of George Schwert in the biochemistry department kindled my interest in biochemistry. After one year of residency on the medical service of Duke Hospital, chaired by Eugene Stead, I joined the group of Arthur Kornberg at Stanford Medical School as a postdoctoral fellow. Two years later I accepted a faculty position at Harvard Medical School, where I remain today. During these 50 years, together with an outstanding group of students, postdoctoral fellows, and collaborators, I have pursued studies on DNA replication. I have experienced the excitement of discovering a number of important enzymes in DNA replication that, in turn, triggered an interest in the dynamics of a replisome. My associations with industry have been stimulating and fostered new friendships. I could not have chosen a better career.

Structure-specific DNA binding by bacteriophage T5 5'-->3' exonuclease

Phage T5 exonuclease is a 5'-->3'exodeoxyribonuclease that also exhibits endonucleolytic activity on flap structures (branched duplex DNA containing a free single-stranded 5'-end). Oligonucleotides were used to construct duplexes with either blunt ends, 5'-overhangs, 3'-overhangs, a flap or a forked end (pseudo-Y). The binding of T5 exonuclease to various structures was investigated using native electrophoretic mobility shift assays (EMSA) in the absence of the essential divalent metal cofactor. Binding of T5 exonuclease to either blunt-ended duplexes or single-stranded oligonucleotides could not be detected by EMSA. However, duplexes with 5'-overhangs, flaps and pseudo-Y structures showed decreased mobility with added T5 exonuclease. On binding to DNA the wild-type enzyme was rendered partially resistant to proteolysis, yielding a biologically active 31.5 kDa fragment. However, the protein-DNA complex remained susceptible to inactivation by p-hydroxymercuribenzoate (PHMB, a cysteine-specific modifying agent), suggesting that neither cysteine is intimately associated with substrate binding. Replacement of both cysteine residues of the molecule with serine did not greatly alter the catalytic or binding characteristics of the protein but did render it highly resistant to inhibition by PHMB.

A new gene of Escherichia coli K-12 whose product participates in T4 bacteriophage late gene expression: interaction of lit with the T4-induced polynucleotide 5'-kinase 3'-phosphatase

We isolated five Escherichia coli mutants deficient in their ability to support the late (replication-coupled) gene expression of T4 bacteriophage at 30 degrees C. These mutants, which we call Lit mutants, define at least one novel gene at 25 min on the E. coli map. They were selected in an attempt to obtain mutants which restrict the growth of T4 mutants deficient in polynucleotide 5'-kinase 3'-phosphatase but not that of wild-type T4 at 37 degrees C. Some of the mutants do have these phenotypes under some conditions. Studies of the block in T4 development in some of the E. coli mutants suggest that Lit mutants are affected in a gene product involved in the metabolism of deoxyribonucleic acid nicks or single-strand gaps. None of the Lit mutants is deficient in the major, bacterial, 3'-phosphatase activity in crude extracts.

Role of the T5 gene D15 nuclease in the generation of nicked bacteriophage T5 DNA

The processing of newly replicated concatameric T5 DNA into both single stranded DNA changed of unit length and single-stranded fragments of sizes comparable to those found in mature T5 virion DNA occurs in the absence of late T5 protein synthesis. The formation of unit-length, single-stranded DNA chains does not require the early T5 gene D15 nuclease: however, the subsequent formation of the single-stranded fragments does require that the D15 nuclease be functional. A reexamination of the properties of the purified D15 nuclease under a variety of conditions showed that, in addition to functioning as a 5' leads to 3' exonuclease, the enzyme can also introduce endonucleolytic scissions into mature T5 DNA in a reaction that requires duplex T5 DNA and preexisting, single-stranded interruptions.

The regulation of transcription in bacteriophage T5-infected Escherichia coli

The expression of bacteriophage T5-specific RNA and protein in infected cells is temporally separated into three classes: class I (preearly), class II (early), and class III (late). By immunoprecipitation techniques we have shown that T5 infection of cells leads to the synthesis of one class I polypeptide (11,000 daltons) and two class II polypeptides (90,000 and 15,000 daltons) capable of binding to the RNA polymerase of the host Escherichia coli cell. One of the class II polypeptides (90,000 daltons) is the product of gene C2, which is an essential gene product required for the initiation of class III RNA synthesis. The colicinogenic factor, ColIb, is a plasmid which prevents the normal synthesis of class II and the III bacteriophage T5-specific RNA in infected colicinogenic (ColIb+) cells. In T5-infected colicinogenic cells, only the T5 class I polypeptide is found associated with the RNA polymerase. Mutants of T5, designated T5h minus, are capable of growth on both noncolicinogenic and ColIb+ hosts. Extracts of T5h minus infected ColIb+ cells were shown to lack a small class I polypeptide (12,000 daltons) as compared to T5-infected cells. The h minus mutation, however, has no effect on the levels of the class I T5 polypeptide of similar molecular weight which is bound to the RNA polymerase. One effect of the h minus mutation is to enhance the quantities of the two class II polypeptides bound to the enzyme.