Dual control of arabinose genes on transducing phage λd ara

Abstract

A λ-φ80 hybrid derivative of the defective transducing phage φ80d ara (Gottesman & Beckwith, 1969) has most of its late genes replaced by Escherichia coli DNA containing an intact arabinose operon. In a cell lysogenic for this phage the arabinose operon on the phage responds normally to its regulatory gene araC and to the level of l-arabinose in the growth medium. However, as a consequence of transcriptional read-through from phage late genes to the arabinose operon, arabinose enzymes are also synthesized under the control of phage gene Q during growth of the phage in the absence of l-arabinose. We also show that the gene araC has the same transcriptional orientation as the phage late genes and the arabinose operon genes B, A and D. Since monomers of phage lysozyme and l-arabinose isomerase are produced in comparable quantities under phage late control, it follows that if there is transcription termination at the end of the gene araC it is no more than 90% efficient.