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. 2006 Sep 12;103(38):13962–13967. doi: 10.1073/pnas.0606384103

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© 2006 by The National Academy of Sciences of the USA

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Fig. 6. — Schematic representation of the postulated regulatory circuits involving IF2 and ppGpp. (Upper) The essential steps of translation initiation: formation of 30SIC in the presence of IF2-GTP (▴), association of 50S subunit and formation of 70SIC, GTP (▴) hydrolysis to GDP (), IF2 dissociation (), and initiation dipeptide formation. Amino acid starvation during elongation triggers RelA-dependent synthesis of ppGpp (■), which inhibits stable RNA transcription (Lower) and, as shown in this study, the initiation functions of IF2 (30SIC formation and initiation dipeptide formation). A possible function of translation initiation intermediates containing IF2-ppGpp () in feedback inhibition of stable RNA transcription is suggested by earlier reports that components of the translation initiation apparatus play an active part in this regulation. In particular, IF2, fMet-tRNA, and ppGpp were found to interact with the RNA polymerase and influence its activity at stable RNA promoters (38, 39), whereas IF2 (40), IF3 (41), and initiation-competent 30S subunits (42) were shown to be required for feedback repression of stable RNA transcription.

Inline graphic — Schematic representation of the postulated regulatory circuits involving IF2 and ppGpp. (Upper) The essential steps of translation initiation: formation of 30SIC in the presence of IF2-GTP (▴), association of 50S subunit and formation of 70SIC, GTP (▴) hydrolysis to GDP (), IF2 dissociation (), and initiation dipeptide formation. Amino acid starvation during elongation triggers RelA-dependent synthesis of ppGpp (■), which inhibits stable RNA transcription (Lower) and, as shown in this study, the initiation functions of IF2 (30SIC formation and initiation dipeptide formation). A possible function of translation initiation intermediates containing IF2-ppGpp () in feedback inhibition of stable RNA transcription is suggested by earlier reports that components of the translation initiation apparatus play an active part in this regulation. In particular, IF2, fMet-tRNA, and ppGpp were found to interact with the RNA polymerase and influence its activity at stable RNA promoters (38, 39), whereas IF2 (40), IF3 (41), and initiation-competent 30S subunits (42) were shown to be required for feedback repression of stable RNA transcription.