A transposable promoter and transposable promoter probes derived from Tn1721

We describe two types of new Tn1721-derivatives capable of random insertion and of generating transcriptional fusions at the site of insertion: transposable promoters (Tn1735) carrying a strong, inducible ptac promoter that turns on adjacent (cryptic) genes; and transposable promoter probes (Tn1736, Tn1737) carrying promoterless genes coding for chloramphenicol acetyl transferase or beta-galactosidase, and used to accurately determine the expression of external promoters. These elements are available with four different selectable resistance markers and on conjugative, temperature-sensitive and multicopy plasmid vehicles. Experiments are described that demonstrate the advantage of random insertions for expressing various genes and for studying gene regulation.