Lambda transducing phages carrying segments of the Escherichia coli chromosome in the dapB region have been isolated in their in vivo gene products analyzed by two-dimensional gel electrophoresis. One of these phages, lambdaddapB-2, carries the structural genes for ribosomal protein S20 (rps T) and isoleucyltransfer RNA synthetase (ileS.) The most likely gene order is thr-rpsT-ileS-dapB-pyrA.