In Vivo and In Vitro Recombination of Small-phage DNAs with Plasmids and Transposable Drug-resistance Elements: Introduction

Abstract

The minichapters that follow have been included as an indication of some of the new directions being taken in small-phage research. The application of both recombinant DNA and transposon techniques, together with the recently developed DNA sequencing techniques, opens up many new and exciting areas of investigation related to the structure and function of small-phage genomes and allows the development of DNA cloning vectors having unique properties.

Studies of insertions into and deletions of filamentous phage genomes show clearly that the size of the virion is determined by the DNA. Miniphage containing extensive deletions of the viral genome form correspondingly smaller virions. Similarly, insertions into the viral genome lead to the production of virions of greater than unit length. Several different transposable drug-resistance elements and even the entire pSC101 plasmid have been inserted into filamentous phage DNA in vivo. Foreign DNAs have also been inserted into specific restriction sites in vitro.

Since for the filamentous phages all genes are essential for phage growth, it would be expected that most transducing phages constructed either by random in vivo insertions or by insertions into restriction sites would be defective. This appears to be the case for the recombinant phages that require a wild-type helper phage for their propagation. Analysis of helper-independent phage, on the other hand, should identify sites where the nucleotide sequence can be interrupted without interfering with the ability of the phage to propagate and to form a plaque. Such sites have already been identified within the intergenic space containing...