Ivanova Natalia, Pavlov Michael Y, Ehrenberg Måns
Department of Cell and Molecular Biology, BMC, Uppsala University, Box 596, S-75 124 Uppsala, Sweden.
J Mol Biol. 2005 Jul 29;350(5):897-905. doi: 10.1016/j.jmb.2005.05.033.
A ribosome stalled on a truncated mRNA in the eubacterial cell can be rescued by tmRNA via a process called trans-translation. We demonstrate here that release of truncated mRNAs from stalled ribosomes accelerates significantly already after trans-peptidation following tmRNA binding to the ribosome. However, rapid release of truncated mRNA requires EF-G-dependent translocation of peptidyl-tmRNA from the A to the P site of the ribosome. We show also that the rate of mRNA release before and after peptidyl-tmRNA translocation correlates well with the rate of dissociation of deacylated tRNA, indicating that mRNA is retained on the ribosome mainly through codon:anticodon interaction with tRNA. The rate of mRNA release is reduced for mRNAs with strong Shine-Dalgarno (SD)-like sequences in the vicinity of the truncation site as well as for mRNAs with long 3' extensions downstream from the P-site codon. The reduced rate of release in the former case was due to a persisting SD-anti SD interaction between mRNA and the ribosome.
在真细菌细胞中，停滞在截短mRNA上的核糖体可通过tmRNA经由一种称为反式翻译的过程得到拯救。我们在此证明，在tmRNA与核糖体结合后的转肽作用之后，截短mRNA从停滞核糖体上的释放就已显著加速。然而，截短mRNA的快速释放需要EF-G依赖的肽基-tmRNA从核糖体的A位点向P位点的易位。我们还表明，肽基-tmRNA易位前后mRNA的释放速率与脱酰基tRNA的解离速率密切相关，这表明mRNA主要通过与tRNA的密码子：反密码子相互作用而保留在核糖体上。对于在截短位点附近具有强的类似Shine-Dalgarno（SD）序列的mRNA以及在P位点密码子下游具有长3'延伸的mRNA，mRNA的释放速率降低。前一种情况下释放速率降低是由于mRNA与核糖体之间持续存在的SD-反SD相互作用。
