Abstract
Regulated transcription termination provides an efficient and responsive means to control gene expression [1]. Intrinsic terminators, which consist of an RNA stem-loop followed by a poly-U tract, catalyze termination by disrupting the RNA polymerase elongation complex [2]. In antitermination, an antiterminator stem-loop is mutually exclusive with the terminator stem-loop [1], [3]. In different contexts, formation of the antiterminator stem-loop is governed by a translating ribosome [1], a ligand-binding riboswitch [4], [5], or a signal-responsive RNA–binding protein [3]. This latter mechanism is illuminated by Ramesh et al. [6], who studied antitermination by a broadly distributed class of signal-responsive RNA-binding proteins containing the ANTAR domain.
Highlights
Studies conducted in the 1990s characterized two related antitermination proteins: AmiR, which regulates aliphatic amide catabolism in Pseudomonas aeruginosa [7,8], and NasR, which regulates nitrate assimilation in Klebsiella oxytoca [9,10]
RNA binding occurs through the carboxyl-terminal ANTAR domain (AmiR and NasR transcription antitermination regulator) [11]
Different ANTAR proteins use a variety of signal input domains, at least half contain a two-component signal transduction receiver domain [6,11]
Summary
Studies conducted in the 1990s characterized two related antitermination proteins: AmiR, which regulates aliphatic amide catabolism in Pseudomonas aeruginosa (amiECBRS operon) [7,8], and NasR, which regulates nitrate assimilation in Klebsiella oxytoca (nasFEDCBA operon) [9,10]. RNA binding occurs through the carboxyl-terminal ANTAR domain (AmiR and NasR transcription antitermination regulator) [11]. AmiR and NasR RNA binding responds to signal input mediated by the amide-binding AmiC protein [12,13] and the nitrate-binding NIT domain [14,15], respectively. AmiR and NasR target the transcribed leader RNA upstream of the amiE and nasF operons, respectively [12,14]. Both leaders encode two obvious stem-loop secondary structures: the distal intrinsic terminator (including a poly-U tract) [2], and P1, a proximal structure essential for antitermination (Figure 1A). Other ANTAR proteins, including AmiR, contain a nonphosphorylated pseudo-receiver domain [13,17]
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