A Novel Complex: A Quantum Dot Conjugated to an Active T7 RNA Polymerase
Figure 5
Activity of QD : T7RNAP complexes tested in a single molecule assay. In the single molecule assay the DNA tether was biotinylated at the free end, thus allowing a streptavidin-coated QD to attach to this end. In the control no ribonucleotides (NTPs) were present. Hence, as the Bio-T7 RNAP requires the initiating nucleotide (GTP) for specific binding to the promoter, it is likely that the QD at the end of the tether is the only QD affiliated with the DNA tether of the control. (a) Intensity distributions of DNA tethers with varying number of QDs attached. Red bars denote an experiment with NTP present (), and green bars denote the control without NTP (). The concentration of Bio-T7 RNAPs was 200 nM in both cases. (b) Sketch of the +NTP experiment where QDs are attached both at the biotinylated end of the tether and as QD : T7RNAP complexes elongating along the tether. (c) Sketch of the −NTP control, only a single QD is attached at the biotinylated 5′ end of the tether. (d) Image of a typical +NTP experiment where QDs are actually seen at different locations along the tether. (e) Image of a typical −NTP control, only a single QD is visible. Scale bars in (d) and (e) are 500 nm.
