Methods for identification of recombinants of phage lambda

Two methods are described which allow the screening of a large number of phage plaques for a specific DNA sequence carried by the phage or a specific antigen produced within the phage plaque. These methods were set up with lambda and lambdalac phages. Phage plaques were transferred onto nitrocellulose filters by desiccation in 0.1 M NaOH, and the lac sequence was detected by hybridization to radioactive lac mRNA. Beta-Galactosidase was detected by reaction with anti-beta-galactosidase immune serum included in the soft agar of the titration plates; the precipitate thus formed was revealed by means of enzyme-coupled antibodies and in situ coloration. These methods are potentially useful for the identification of lambda transducers, including those which are generated by in vitro recombination with eukaryotic DNA.