Properties of bacterial virus phi A and its DNA

Studies on electrotransfer of DNA into Escherichia coli: effect of molecular form of DNA

Effects of several molecular forms of DNA were examined on voltage-pulse-mediated transfection or transformation. Among circular DNAs, the single-stranded microvirid DNA was less infective than the double-stranded replicative form, whereas transfectivity of the relaxed or nicked molecule was nearly equal to or slightly lower than that of the supercoiled DNA. The linearized double-stranded DNA derived from phage or plasmid electrotransfects Escherichia coli, albeit at a reduced efficiency. Alkaline denaturation of the linearized DNA resulted in complete loss of the infectivity. Relationship between terminal structure of the linearized DNA and efficiency of the transfection was investigated. Host recombination function did not significantly affect the infectivity of the linearized DNA.

DNA transfection of Escherichia coli by electroporation

Electroporation was applied to transfection and transformation of Escherichia coli. Efficient transfer of DNA was achieved by a single voltage pulse at 2.5 kV (initial electric field strength = 6.25 kV/cm), with a 25 microF capacitor. As the recipient for transfecting DNA in the electroporation, spheroplasts, EDTA-treated cells and osmotically shocked bacteria were inferior to intact E. coli. Various parameters affecting the transfection efficiency were defined including growth phase of recipient cells, concentrations of DNA and cells, temperature and additions. In most strains tested, electroporation was far more efficient than Ca2+-dependent transfection (transformation). Various aspects of the electroporation-mediated DNA uptake are discussed.

Conversion of bacteriophage G4 single-stranded viral DNA to double-stranded replicative form in dna mutants of Escherichia coli

Host functions involved in synthesis of parental replicative form of bacteriophage G4 were investigated using various replication mutants of Escheria coli. In dna+ bacteria, conversion of single-stranded viral DNA to replicative form DNA was insensitive to 200 microng/ml of rifampicin or 25 microng/ml of chloramphenicol. At high temperature, synthesis of parental replicative form was unaffected in mutants thermosensitive for dnaA, dnaB, dnaC(D), dnaE or dnaH. In dnaG or dnaZ mutants, however, parental replicative from DNA synthesis was clearly thermosensitive at 43 degrees C. Although the host rep product was essential for viral multiplication, the conversion of single stranded to replicative form was independent of the rep function.

Host genes involved in the replication of single-stranded DNA phage phiK

Using various replication mutants of E. coli, the host genes that participate in the replication of some K12-specific single-stranded DNA phages have been determined. Functional products of dnaE, -F, -G and -Z genes are required for the multiplication of phiK, whereas dnaA, -B, -C(D), H, -I and -P are dispensable for viral replication. In contrast with polB, recA, B, C, or xth functions, host rep activity is essential for phiK. At the restrictive temperature, the yield of phiK was markedly reduced in the ligts7 mutant and partially decreased in a polAts strain. The phage phiK is thus less dependent on the host cells than phiX174 and phiA which require additionally the dnaB, -C(D) and -H functions. Replication of phage St-1 depends on dnaG and -Z gene products, but not on dnaP function. Although not much affected in polAts host, growth of St-1 was significantly diminished in dnaF or ligts7 mutants.

Replication of phiA and phiX174 in Escherichia coli mutants thermosensitive in DNA synthesis

Thermosensitive mutants of E. coli defective in DNA replication were tested for their capacity to support multiplication of phiA and phiX174. At the restrictive temperature, the viral growth was markedly affected in dnaH, dnaZ, or ligts7 mutants. Even when these strains were transfected with RF1 molecules, the virus yield was still very low. The dnaI function was, however, dispensable for replication of phiA and phiX174. In addition, these viruses could multiply in dnaP or polAts mutants at the high temperature.