Characterization of mycobacteriophage I8 and its unrelatedness to mycobacteriophages I1, I3 and I5.

Homology among the genomes of mycobacteriophages I1, I3, I5 and I8 has been studied. Based on restriction endonuclease cleavage patterns, dot blot hybridization and Southern blot hybridization analysis, the DNAs of phages I1, I3 and I5 have been shown to be homologous and indistinguishable, but entirely different from phage I8. Unlike the others, the I8 genome does not harbour any single-strand interruptions. The DNA is 43 kb in length with limited cyclic permutations and has a G + C content of 54%. The presence of 5-methylcytosine in I8 DNA was indicated from the restriction patterns of MspI and HpaII. The number of sites and fragment sizes for several restriction enzymes on I8 DNA has been determined. Phage I8 has a replication cycle of 300 min, with a latent period of 180 min, a rise period of 120 min and a burst size of 100. The viability of phage I8 is significantly reduced by treatment with organic solvents.