Analysis of defective bacteriophages in Escherichia Coli strain 15 derivatives by restriction endonuclease digestion and SDS-polyacrylamide gel electrophoresis
Okazaki, Diane H.
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CsCl isopycnic density gradient centrifugation of lysates of UV- induced cultures of Escherichia coli strain 15 derivatives E. coli 15T- (thy) and E. coli 15 TAU (thy, arg, ura), yielded three phage peaks with buoyant densities of 1.509 g/cm³ (coliphage CP15A), 1.482 g/cm³ (CP15B), and 1.464 g/cm³ (CP15C). Agarose gel electrophoresis of EcoRI, HindiII, and BamHI endonuclease digests of the DNA from these three defective phage types yielded different digestion patterns, implying a unique genome for each phage type. Molecular weight estimates of genome size by agarose gel electrophoresis were 28 x 10⁶ daltons for CP15A, 26 x 10⁶ daltons for CP15B, and 25 x 10⁶ daltons for CP15C. Although the genomes are different, SDS-polyacrylamide ael electrophoresis revealed that the structural proteins of the tailed phages CP15B and CP15C were similar, whereas the CP15A proteins produced an entirely different pattern. The 65.8 x 10⁶ dalton Pl-like plasmid reported by Ikeda et al. (1970) was observed in agarose gels of two E. coli 15 derivatives.