Interaction between erythrocyte band 3 and the membrane skeleton was analyzed at a level of individual molecules. By observing the movement of band 3 molecules and by dragging the membrane skeleton using optical tweezers, it was found that the cytoplasmic portion of band 3 collides with the membrane skeleton, which causes temporal confinement of band 3 within a mesh of spectrin network of-100nm ∅. Band 3 hops to an adjacent mesh at an average of once every 350 ms. These results demonstrate that single molecule observation/manipulation techniques provide unique and valuable tools for the study of living cells.
Transcription initiation is a multi-step reaction. The conventional model is sequential, but fails to explain kinetic behaviors of abortive syntheses from some promoters, existence of inactive transcription complex, and different yields of full-length transcripts in vitro from different promoters. These are explained by a new model which is derived from our kinetic study on abortive synthesis. This new model has two branched pathways; one leads to fulllength synthesis and the other to inactivation via a transcription complex which produces only abortive transcript. This model may help the structural understanding of transcriptional regulation of both initiation and elongation, which is based on recent progress in structural biology of transcription like bending of DNA template, apparent discontinuous movements of RNA polymerase, and different spatial relationship among catalytic center, RNA and DNA.
Arrays of microgrooves (width 6, 7, and 8 μm; depth 4.5μm; length 10, 20, 30, 40, and 100μm; number 2600 or 4704 in parallel) photofabricated in the surface of a single-crystal silicon substrate were converted to arrays of leak-proof microchannels by tightly covering them with an optically flat glass plate. Using the microchannels as a model of physiological capillaries, total flow rate of blood was determined under a constant suction while flow behavior of blood cells in each channel was microscopically observed. Erythrocyte deformability, leukocyte adhesiveness, and platelet aggregability quantified by channel transit time or channel blocking and reopening rates showed changes caused by environmental factors such as diet and exposure to bacterial cells.