Identification of a second tetracycline-inducible polypeptide encoded by Tn10

Abstract

Three Tn10 polypeptides were detected by analyzing the proteins synthesized in ultraviolet light-irradiated Escherichia coli cells after infection with lambda::Tn10. One of these polypeptides was the previously identified 36,000-dalton TET polypeptide. The other two had approximate sizes of 25,000 and 13,000 daltons. The syntheses of both the TET polypeptide and the 25,000-dalton polypeptide were inducible by tetracycline in lambda-immune hosts. Similarly, the synthesis of the TET polypeptide was inducible in nonimmune hosts. However, the synthesis of the 25,000-dalton polypeptide was constitutive in nonimmune hosts. An amber mutation in a gene required for tetracycline resistance on lambda::Tn10 was isolated that eliminated the synthesis of the TET polypeptide in sup+ hosts but not the synthesis of the 25,000-dalton or the 13,000-dalton polypeptides. The expression of tetracycline resistance from wild-type Tn10 was found to be anomalous in E. coli strains carrying the amber suppressors supD, supE, and supF. In general, strains containing these nonsense suppressors were less resistant to tetracycline.

A multifunctional gene (tetR) controls Tn10-encoded tetracycline resistance

“…When tested in a minicell system, these mutant plasmids no longer coded for the synthesis of a 23,000-dalton protein. This protein is presumably identical to the TnlO-encoded, tetracyclineinducible 23,000and 25,000-dalton polypeptides bserved previously (40,42). The TetA protein Fractionation of inner and outer membranes by sucrose density gradient centrifugation of membranes prepared from strain CB118, which carries plasmid pCB27.…”

“…It was deduced from studies with tet-lacZ fusion mutants that the tet regulatory region is involved in the regulation of at least two tet genes (6). Zupancic et al (42) detected two TnlO-encoded proteins (molecular weights, 36,000 and 25,000) whose syntheses are induced by tetracycline. Regulatory mutants of TnlO that express tetracycline resistance constitutively have been isolated (10)(11)(12).…”

Identification of repressor binding sites controlling expression of tetracycline resistance encoded by Tn10

“…Instead, the resistance mechanism appears to involve the active efflux of tetracycline from the cell (1,21). In addition, decreased ribosomal sensitivity to tetracycline may contribute to resistance (17,28).…”

“…The expression of tetracycline resistance is regulated; preincubation with a subinhibitory concentration of tetracycline increases the level of resistance (13). TnJO directs the synthesis of two tetracycline-inducible proteins with apparent molecular weights of 36,000 and 25,000 (26)(27)(28). The largest is referred to as the TET protein and is known to be negatively regulated by a repressor which is inactive in the presence of tetracycline (27).…”

Tetracycline resistance transposon Tn1721: recA-dependent gene amplification and expression of tetracycline resistance

“…In all of these cases resistance is mediated by antibiotic-inactivating enzymes. The gene dosage relationship is rather more complicated in tetracycline resistance, which involves membranebound proteins (20,35,41), up to three synergistically acting resistance mechanisms (34), and delicate genetic control (7,19,40). Members of TetB class, notably TnlO, exhibit decreasing levels of Tcr when gene dosages are increased (16,37); this negative gene dosage effect is now interpreted as the consequence of a regulatory mechanism which prevents overproduction of the major resistance protein (D. C. Coleman and T. J.…”