Control of gene expression through coupling of transcription and translation

Abstract

Transcription and translation form the basis of gene expression in all cells. In prokaryotes they are linked both spatially and temporally as the ribosomes begin translation of the RNA before the RNAP has finished transcribing the entire region, a process known as coupling. Interplay between the two machineries is highly complex and plays an important role in gene expression. To date, most of the studies into transcription-translation coupling have been carried out in vivo, and have focused on the indirect interactions such as attenuation. Due to the many accessory factors for both transcription and translation present within the cell, there is currently no known technique to study direct interactions between the RNAP and the ribosome. Recently, an in vitro transcription-translation system was developed in our lab that is formed from only the pure components required for transcription and translation. This allows the stepwise control of the RNAP and the ribosome. The aim of this study was to determine how close the RNAP and the ribosome can become on the same nascent RNA. The coupled in vitro system was redesigned and optimised to measure the distance between the actively transcribing RNAP and the ribosome translating the same transcript. We show that the ribosome can approach the RNAP as close as 26 nts between the A-site of the ribosome and the active site of the RNAP. This distance is far shorter than was previously thought and reveals a very close contact between the two machineries.