Tn554—a site-specific represser-controlled transposon in Staphylococcus aureus

Abstract

PREVIOUS studies have defined a specific element in Staphylococcus aureus containing determinants of inducible erythromycin resistance and spectinomycin resistance. This element has many plasmid-like properties^1,2 but is not associated with detectable extra-chromosomal DNA². The resistances are similar in mechanism to those ordinarily associated with plasmids^3,4 (J. Davies, personal communication); the element can be transferred by transduction² or transformation to a rec⁻ recipient with the same efficiency as to a rec⁺, and the two determinants show essentially 100% linkage in genetic transfer. Consequently, this linkage group has previously been referred to as a ‘pseudoplasmid’ (ref. 2). On the basis of the results presented here, we suggest that this pseudoplasmid is actually the prototype of a new class of transposon, which functions by means of a highly efficient, represser-controlled, site-specific integration–excision mechanism. This transposon, designated Tn554 (EmSp), can be most easily envisaged as a prophage-like element that lacks replicative autonomy and other vegetative phage functions.