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In vitro studies have been of great value in elucidating the mechanism of the regulation of several bacterial operons. To obtain a deoxyribonucleic acid preparation enriched for the histidine ( his ) and for the isoleucine-valine ( ilv ) operons, we have isolated bacteriophages carrying the his and the ilv regions of the Escherichia coli chromosome. Transposition of the his operon to a site close to the att80 region of the E. coli chromosome has been carried out selecting for integration of a temperature-sensitive F′ his + in the tonB locus. This transposed strain has been lysogenized with φ80i λ . Upon induction of the lysogen, His + transductants have been isolated, which, on further induction give rise to HFT (high frequency of transduction) lysates. Preliminary characterization of the transducing phage is reported. The ilv operon, carried on an F′ particle, has been fused to an episome carrying the att80 region. The fused episome has been lysogenized with φ80i λt68. Upon induction of the lysogen, Ilv + transductants have been isolated which on further induction give rise to HFT lysates.

An in vitro system was developed for transcription of the histidine operon of Esherichia coli carried in the genome of a defective 480 transducing phage.The messenger RNA (mRNA) of the histidine operon synthesized in the in vitro system was detected by hybridization to single strands of both 480 and q580dhis DNA, and by competition of this hybridization with unlabeled histidine mRNA that had been synthesized in vivo (RNA extracted from cells in which the histidine operon had been derepressed

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