Tn4371: A modular structure encoding a phage-like integrase, a Pseudomonas-like catabolic pathway, and RP4/Ti-like transfer functions

Tn4371 is a 55-kb catabolic transposon originally isolated from Ralstonia eutropha A5 that encodes enzymes catalyzing the complete degradation of biphenyl. Unlike previously described transposons encoding similar genes for aromatic compound degradation. Tn4371 carries a phage-like degradation, Tn4371 integrase gene and RP4/Ti-like transfer genes. Tn4371 transposition involves an excision/integration process and, consistent with this site-specific recombination mechanism, the ends of the element are transiently covalently bound. Transposition is targeted to a limited number of sites on the CH34 chromosome and pMOL30 plasmid as well as on RP4. One of these sites consists of a 5'-TTTTTCAT-3' sequence which is also present between the covalently joined ends of the transposon. Conjugative transfer of Tn4371 could not yet be demonstrated although the functionality of its transfer machinery could be established through the identification of a second transposable element, Tn-bph, which contains the right half of Tn4371, including the bph catabolic gene cluster and the identified transfer genes. Tn-bph transfers by conjugation and integrates in a new host genome independently of the larger element. Tn4371 thus appears as composite transposon combining an enteric phage-like integration system, RP4/Ti-like conjugation genes, and Pseudomonas-like catabolic genes.