Team:SUSTC-Shenzhen-B/introduction

Introduction

Transcription：

The transcription stage, the reading of genetic information from DNA, is composed of promoter binding and the activation of RNA polymerase, RNA transcript initiation and promoter escape, RNA transcript elongation, and transcript termination, and release.

What is terminator?

Terminators are genetic parts that usually occur at the end of a gene or operon and cause transcription to stop. In prokaryotes, terminators usually fall into two categories (1) rho-independent terminators and (2) rho-dependent terminators.

Rho-independent terminators are generally composed of palindromic sequence that forms a stem loop rich in G-C base pairs followed by several T bases. The conventional model of transcriptional termination is that the stem loop causes RNA polymerase to pause and transcription of the poly-A tail causes the RNA:DNA duplex to unwind and dissociate from RNA polymerase.

Terminator Efficiency：

Although terminators are positioned at the ends of genes, they also play irreplaceable roles. It is important that transcription is imperfectly terminated at some terminator so that the ratio of the amount of the mRNA transcribed from upstream and that from downstream of the terminator is controlled. This regulation is qualified by the termination efficiency.

Brief idea to calculate efficiency:

The fluorescence produced by the characterization devices are then measured using flow cytometry to calculate the termination efficiency of the terminators.

E=1-S/T

E: Terminator efficiency

S: The number of transcription events that the transcription is not terminated by terminator, therefore transcription continues to downstream region.

T: The number of total transcription events.

In figure above, we show our experiment design to measure terminator efficiency. A terminator is placed between RFP and GFP gene, and the RFP is the upstream gene. If the terminator is 100% efficient, then, RFP will be transcripted while GFP should not be transcripted. If the terminator is 0% efficienct, then, both RFP and GFP will be transcripted at the same time.