Tagetitoxin inhibits transcription by stabilizing pre-translocated state of the elongation complex.
Transcription elongation consists of repetition of the nucleotide addition cycle: phosphodiester bond formation, translocation and binding of the next nucleotide. Inhibitor of multi-subunit RNA polymerase tagetitoxin (TGT) enigmatically slows down addition of nucleotides in a sequence-dependent manner, only at certain positions of the template. Here, we show that TGT neither affects chemistry of RNA synthesis nor induces backward translocation, nor competes with the nucleoside triphosphate (NTP) in the active center. Instead, TGT increases the stability of the pre-translocated state of elongation complex, thus slowing down addition of the following nucleotide. We show that the extent of inhibition directly depends on the intrinsic stability of the pre-translocated state. The dependence of translocation equilibrium on the transcribed sequence results in a wide distribution (~1-10(3)-fold) of inhibitory effects of TGT at different positions of the template, thus explaining sequence-specificity of TGT action. We provide biochemical evidence that, in pre-translocated state, TGT stabilizes folded conformation of the Trigger Loop, which inhibits forward and backward translocation of the complex. The results suggest that Trigger Loop folding in the pre-translocated state may serve to reduce back-tracking of the elongation complex. Overall, we propose that translocation may be a limiting and highly regulated step of RNA synthesis.
Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Baddiley-Clark Building, Richardson Road, Newcastle upon Tyne NE2 4AX, UK.
Yulia
Y
Yuzenkova
Mohammad
M
Roghanian
Aleksandra
A
Bochkareva
Nikolay
N
Zenkin
D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D003998:Dicarboxylic Acids / Q000494:pharmacology*; D011756:Diphosphates / Q000378:metabolism; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology*; D009943:Organophosphorus Compounds / Q000494:pharmacology*; D061805:Transcription Elongation, Genetic / Q000187:drug effects*; D035602:Transcriptional Elongation Factors / Q000378:metabolism
D003998:Dicarboxylic Acids; D011756:Diphosphates; D019384:Nucleic Acid Synthesis Inhibitors; D009943:Organophosphorus Compounds; D035602:Transcriptional Elongation Factors; C107241:diphosphoric acid; C062221:tagetitoxin; D012321:DNA-Directed RNA Polymerases