Cloning cassettes containing the reporter gene xylE.

Two pUC-derived vectors containing the promoterless xylE gene (encoding catechol 2,3-dioxygenase) of Pseudomonas putida mt-2 were constructed. The t(o) transcriptional terminator of phage lambda was placed downstream from the stop codon of xylE. The new vectors, pXT1 and pXT2, contain xylE and the t(o) terminator within a cloning cassette which can be excised with several endonucleases. When inserted into a transcribed sequence, this xylE cassette reports promoter activity and interrupts downstream transcription of the target sequence.