The Filamentous Phages as Transducing Particles

Abstract

An important property of the filamentous phages is that the length of the virion is determined by the size of the viral DNA molecule encapsulated within it. This conclusion is based on the discovery of miniphage particles, which were shown to contain the viral DNA of deletion mutants (Griffith and Kornberg 1974; Enea and Zinder 1975; Hewitt 1975). For example, the f1 deletion mutant MP-2, which consists of only about 20% of the f1 genome, is found in a phage particle whose length is about 20% that of the wild-type particle (Enea et al. 1977; see also Wheeler and Benzinger, this volume). Particles larger than unit length are also found in all filamentous stocks. Diploid particles constitute about 5% of a wild-type phage population (Scott and Zinder 1967; Salivar et al. 1967). In addition, under permissive conditions, certain amber mutants produce very large, multi-unit-length particles (Pratt et al. 1969). However, nearly all of these multi-unit-length particles, whether they be in wild-type or amber stocks, contain the corresponding number of unit-length DNA molecules. Nevertheless, the existence of greater-than-unit-length phages suggests that filamentous particles containing DNA molecules larger than that of the wild-type f1 genome should be possible. We set out to prove this supposition and, in addition, to determine whether there is a practical limit on how large a DNA molecule can be and yet still be replicated efficiently and extruded as a filamentous phage particle. In our experiments we took advantage of the observation that recombination between apparently nonhomologous DNA...