Final Activity Report Summary - BIOMACHINES BIOWIRES (Biomolecular machines and wires) The work supported by this grant supported the construction of special, ultra-sensitive light microscopes and their use in studies of how tiny biological machines work and how DNA (the molecule that stores genetic information) can be used to transport electricity or energy or to detect proteins and other important biomolecules. The microscopes, which we refer to as 'single-molecule fluorescence microscopes', are designed to allow observation of individual ('single') fluorescent molecules in a miniscule detection zone (as opposed to conventional microscopes that require thousands or millions of molecules to be present in a detection zone). An additional unique feature of the microscopes rests on the fact that two or three lasers are used in rapid alternation (much faster than the average time that one molecule spends in the detection zone) for the detection and the analysis of single molecules; this format carries many advantages compared to the single-laser version of the microscope. This multi-laser microscope allows us to determine the number of parts that make up a particular biological machine, to measure how strong the parts bind to each other, how far apart the parts are spaced and at what orientation, and what are the movements of the parts when the tiny biological machine works. We used our special microscopes to understand processes that occur during gene expression, the path that leads from genetic information (stored in DNA) to the manufacturing of proteins (the molecules that make up most of the machines and structures of living cells). Specifically, we focused on gene transcription, which uses machines that read DNA and copy the information into a messenger molecule (messenger RNA). We also studied the process of gene silencing, which uses machines that recognise and destroy messenger RNA. We use our special microscopes to develop strategies that allow DNA molecules to act as tiny 'wires' that conduct electricity and energy; these DNA-based wires can be useful in building smaller and more efficient electronic circuits. DNA was also central in the most important contribution of this work, since it was used as a biosensor for identifying and measuring the concentration of specific proteins known as transcription factors. Transcription factors are proteins that control transcription and therefore control the levels of messenger RNA and of proteins in cells and thus are important for the development, maintenance and environmental sensing of every living cell. Detecting the presence and concentration of transcription factors is important for developing diagnostic assays that are extremely useful for making decisions about medical treatments and therefore can help promote human and animal health.