Effect of the dnaN mutation on the growth of small DNA phages.

The effect of the dnaN mutation on the growth of single-stranded DNA phages was studied by burst experiments. In HC138 dnaN cells exposed to 42.5 degrees C at 5 min before infection, growth of spherical (microvirid or isometric) phages such as alpha 3, phi Kh-1 and phi X174 was partially reduced at the nonpermissive temperature. When infection was performed at 30 min after temperature shift-up, viral replication was completely inhibited at 42.5 degrees C in the dnaN strain but not in a dna+ revertant. At 41 degrees C, multiplication of filamentous (inovirid) phages M13 and fd was restricted specifically in HC138 F+ dnaN bacteria. When dnaN cells lysogenic for lambda i21 were grown at 42.5 degrees C for 60 min and then shifted down to 33 degrees C, a burst of lambda i21 occurred with concomitant cellular lysis, manifesting induction of the prophage development.