Mapping of new Escherichia coli K and 15 restriction sites on specific fragments of bacteriophage phi X174

Small size, big impact: how studies of small DNA tumour viruses revolutionized biology

Intense study of three families of small tumour viruses with double-stranded DNA genomes, carried out over 50 years, has had a profound impact on biology. The polyomaviruses and papillomaviruses have circular DNA genomes of approximately 5000 and approximately 8000 base-pairs, respectively, and thus encode only a handful of proteins. Adenoviruses have a 32 000-base-pair linear DNA genome, still far smaller than the three billion-base-pair human genome. Members of all three virus families can transform cultured cells to tumorigenicity and cause tumours in experimental animals. Several human papillomaviruses (HPV) and at least one polyomavirus are oncogenic in humans. Early analysis of these viruses, particularly the polyomavirus SV40, led to the development of many powerful experimental tools, including restriction mapping, site-directed mutagenesis, gene transfer, genome-wide sequencing and recombinant DNA. These tools have since been refined and used to study cellular genes, revolutionizing our understanding of biology. These tools were also applied to the viruses themselves. Analysis of the virus life cycle and the effect of these viruses on cells yielded important new insights into many aspects of gene expression, DNA replication, cell biology and carcinogenesis. These studies have also led to vaccination strategies to prevent infection and cancer in humans. This article is part of the theme issue 'Silent cancer agents: multi-disciplinary modelling of human DNA oncoviruses'.

Structures and mechanisms of DNA restriction and modification enzymes

DNA restriction and modification enzymes are responsible for the hostspecific barriers to interstrain and interspecies transfer of genetic information that have been observed in a variety of bacterial cell types. Although the phenomenon of host specificity was initially observed in the early 1950s (Luria & Human, 1952; Bertani & Weigle, 1953), it was nearly a decade later that Arber and his colleagues accurately predicted the molecular basis of the phenomenon. Their experiments with bacteriophage λ demonstrated that a given host-specificity system imparts a specific modification to the viral DNA, and further, that restriction of DNA lacking the appropriate modification is s consquence of nucleolytic hydrolysis upon entry into the host cell (Arber & Dussoix, 1962; Dussoix & Arber, 1962; Arber, Hattman & Dussoix, 1963).

Transfection of Enterobacteriaceae and its applications

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DNA synthesis in vitro dependent upon phiX174 replicative form I DNA

Extracts of Escherichia coli strains infected with bacteriophage phiX174 catalyze DNA synthesis dependent on double-stranded, circular phiX174 replicative form I (phiX RFI) by a semiconservative process. The reaction required Mg++, ATP, all four dNTP, and exogenous phiX RFI DNA as template and yielded phiX RFI and phiX RFII. The reaction was inhibited by nalidixic acid and novobiocin but not by rifampicin. DNA synthesis required the phiX174 gene A product and E. coli gene products dnaB, dnaC(D), dnaG, and rep.

Specific cleavage analysis of mammalian mitochondrial DNA

Mitochondrial DNA from several mammalian species has been digested with a site-specific restriction endonuclease (HaeIII) from Haemophilus aegyptius. A quantitative analysis of the resulting specific fragments indicates that the mtDNA of any individual mammal is predominantly a single molecular clone. Gel analysis of specific cleavage products has proven quite sensitive in detecting differences in mtDNA: mtDNAs from the more distantly related mammals studied (e.g., donkey and dog) are found to have few bands in common and very closely related mammals (e.g., donkey and horse) share only about 50% of their bands. This procedure has detected several intraspecies mtDNA differences. Six distinct human patterns have been found, with one pattern usually differing from another in two or three bands. mtDNAs from different organs of single individuals have also been analyzed, and no differences have been found.

Fragment maps of phiX-174 replicative DNA produced by restriction enzymes from haemophilus aphirophilus and haemophilus influenzae H-I

phiX-174 replicative form (RF) DNA was cleaved by restriction enzymes from Haemophilus aphirophilus (Hap) and H. influenzae (H-I strain Osaka) (HinH). Five fragments were produced by Hap and eight by HinH. The positions of all of the Hap fragments and six of the HinH fragments were mapped on the genome by heteroduplex transfection and DNA-DNA hybridization methods. In addition, fragment sizes of phiX-174 RF DNA and S13 RF DNA by Hap and HinH were compared. Considerable differences of the size of the fragments produced from these closely related phage genomes were observed.

Isolation and function of the gene A initiator of bacteriophage phi-chi 174, a highly specific DNA endonuclease

The gene A product of Escherichia coli bacteriophage varphiX 174, necessary for initiation of varphiX DNA synthesis, has been identified and purified to near homogeneity. The gene A protein is shown to be a highly specific DNA endonuclease which breaks one phosphodiester bond in the viral strand of either double-stranded, circular varphiX replicative form I (RFI), or in single-stranded, circular varphiX viral DNA; it is inactive against all other species of DNA tested.