Evolution of complex resistance transposons from an ancestral mercury transposon

Abstract

The molecular interrelationship of a transposon family which confers multiple antibiotic resistance and is assumed to have been generated from an ancestral mercury transposon was analyzed. Initially, the transposons Tn2613 (7.2 kilobases), encoding mercury resistance, and Tn2608 (13.5 kilobases), encoding mercury, streptomycin, and sulfonamide resistances, were isolated and their structures were analyzed. Next, the following transposons were compared with respect to their genetic and physical maps: Tn2613 and TnSOJ, encoding mercury resistance; Tn2608 and Tn21, encoding mercury, streptomycin, and sulfonamide resistance; Tn2607 and Tn4, encoding streptomycin, sulfonamide, and ampicillin resistance; and Tn2603, endocing mercury, streptomycin, sulfonamide, and ampicillin resistance. The results suggest that the transposons encoding multiple resistance were evolved from an ancestral mercury transposon.

Transposon targeting determined by resolvase

“…RP1 [14]) whereas others belong to class 2 transposons including TnpR of Tn 21 [19]. The postulated Tn 21 ancestor, Tn 2613 [20], and another similar progenitor element [21] are supposed to have attracted independent insertions of Tn 5090 /Tn 402 into equivalent internal sites close to res to form Tn 21 and Tn 1403 , respectively.…”

Tn5060from the Siberian permafrost is most closely related to the ancestor of Tn21prior to integron acquisition

“…Stanisich cited by Brown et al [11]), which indicates that the present evolutionary model is valid. However, since the ¢rst model for the evolution of Tn21 was proposed in 1983 [17], no appropriate candidate for TnX has been found amongst the sequenced Tn21 subgroup transposons lacking integrons [18^21]. Compared to Tn21, these transposons had too many di¡erences which have not permitted the presumed structure of TnX to be inferred from either of them.…”

Structure and function of hot spots providing signals for site‐directed specific recombination and gene expression in Tn21 transposons

“…aadB in Jr\4000, bta (PSE) in Jn2101) (Schmidt ef at., 1988 and unpublished results), deletion (aadA in pBP215) (Schmidt, 1984) and substitution (bta (OXA) in Tn2410) (Schmidt, 1984) of these Tn,?7-related structures were congruent within the limit of detection (^ZO nucleotides) at both ends of aadA. The existence of such recombinational hot spots has been confirmed by others (Grinsted ef at., 1982;Tanaka et al, 1983;Martinez and de taCruz, 1988;Schmidt etai, 1988).…”