Working with Phage P22.

Transduction experiments in <i>Escherichia coli</i> and <i>Salmonella</i> are usually performed with virulent phage variants. A widely used P1 mutant, called P1 <i>vir</i>, carries one or more uncharacterized mutations that prevent formation of lysogens. In the case of P22, by far the most frequently used variant is named P22 HT105/1 <i>int-201</i> This phage has a high transducing (HT) frequency due to a mutant nuclease with lower specificity for the <i>pac</i> sequence. As a result, ∼50% of the P22 HT phage heads carry random transducing fragments of chromosomal DNA. The <i>int</i> mutation reduces the formation of stable lysogens. The basic steps in handling the P22 HT105/1 <i>int-201</i> phage and in performing transduction experiments in <i>Salmonella</i> are described here.