DNA of Myxococcus bacteriophage MX-1: macromolecular properties and restriction fragments

Abstract

1. Bacteriophage MX-1 is a virulent DNA phage whose hosts include strains of Myxococcus xanthus, M. fulvus and M. virescens. DNA was extracted from purified phage preparations. The molecular weight of phage DNA was measured by sedimentation-velocity and by rate-zonal ultracentrifugation. The apparent molecular weight was found to vary for reasons discussed in the text. From rate-zonal ultracentrifugation, using calibrated sucrose gradients, the molecular weight was calculated to be 149 (+/-22) X 10(6) daltons. The base composition of the DNA was estimated by different methods and was found to be 50-52% (G + C). The DNA demonstrated an anomalous thermal denaturation profile in dilute buffer. Denatured DNA was fractionated by ion-exchange chromatography and by buoyant-density centrifugation. No significant strand separation was obained and it was concluded that overall base compositions of the two strands are very similar. 2. DNA from bacteriophage MX-1 was hydrolysed with restriction endonucleases R. EcoRI, R.EcoRII and R. HindIII. The restriction fragments were catelogued and their apparent molecular weights calculated from electrophoresis gels calibrated with fragments from the DNA of coliphage lambda. From the total fragments obtained with nuclease R.EcoRI, the minimum apparent molecular weight of MX-1 DNA was found to be 130 X 10(6) daltons.