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Abstract
tRNA-mediated transcription antitermination has been shown to control the expression of several amino acid biosynthesis operons and aminoacyl-tRNA-synthetase-encoding genes in Gram-positive bacteria. A model originally put forward by Grundy & Henkin describes the conserved structural features of the leader sequences of these operons and genes. Two sequences of 3 and 4 nt, respectively, take a central position in this model and are thought to be responsible for the binding of the system-specific uncharged tRNA, an interaction which would stabilize the antiterminator conformation of the leader. Here a further evolution of this model is presented based on an analysis of trp regulation in Lactococcus lactis in which a function is assigned to hitherto unexplained conserved structures in the leader sequence. It is postulated that the mRNA–tRNA interaction involves various parts of the tRNA in addition to the anticodon and the acceptor in the original model and that these additional interactions contribute to the recognition of a specific tRNA, and hence to the specificity and efficacy of the regulatory response.
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