| In all living organisms, genetic information stored in DNA directs the synthesis of RNA via a process termed transcription. This RNA can then either fold into a catalytically active ribozyme, act as the template for the construction of proteins, or serve a variety of other cellular functions. The enzyme responsible for carrying out DNA transcription---RNA polymerase (RNAP)---therefore plays a central role in cells, so it is hardly surprising that process of transcription is both complex and highly regulated. In bacteria such as E. coli , for example, over 100 factors have been identified that modify RNAP. During transcription, RNAP navigates a complex biochemical landscape which has not been fully characterized and includes transitions associated both with elongation of RNA and with regulatory pause states. Several of these biochemical transitions are coupled to changes in the mechanical state of the enzyme, such as the position of RNAP relative to the DNA template. Understanding the nature of these mechanical transitions is crucial in developing a complete view of transcription, but the mechanical states of RNAP have been difficult to observe directly in the past. To better characterize the process of transcription by RNAP, we constructed the first optical trapping apparatus capable of measuring displacements as small as a single Angstrom in individual molecules. By monitoring the mechanics of transcription by RNA polymerase and assigning biochemical roles to the observed transitions, we demonstrate that single-molecule techniques offer unique insights into this complex process. |
