First peek at DNA transcription.For the first time, researchers have recorded molecular-scale images of the initial step in a process crucial to living cells-the use of genetic information contained in DNA DNA: see nucleic acid. DNA or deoxyribonucleic acid One of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes. . Neil H. Thomson of the University of California, Santa Barbara History The predecessor to UCSB, Santa Barbara State College, focused on teacher training, industrial arts, home economics, and foreign languages. Intense lobbying by an interest group in the City of Santa Barbara led by Thomas Storke and Pearl Chase persuaded the State and his coworkers have produced sequences of micrographs that show an enzyme molecule straddling a strand of DNA and pulling it along to complete the beginning phase of protein manufacture. Thomson described the research last week at an American Physical Society The American Physical Society was founded in 1899 and is the world's second largest organization of physicists. The Society publishes more than a dozen science journals, including the world renowned Physical Review and Physical Review Letters, and organizes more than twenty science meeting in Kansas City, Mo. "We're seeing the opening of a new field of biophysics biophysics, application of various methods and principles of physical science to the study of biological problems. In physiological biophysics physical mechanisms have been used to explain such biological processes as the transmission of nerve impulses, the muscle , based on locating, isolating, attaching, and manipulating single molecules," says Carlos Bustamante of the Institute of Molecular Biology molecular biology, scientific study of the molecular basis of life processes, including cellular respiration, excretion, and reproduction. The term molecular biology was coined in 1938 by Warren Weaver, then director of the natural sciences program at the Rockefeller at the University of Oregon The University of Oregon is a public university located in Eugene, Oregon. The university was founded in 1876, graduating its first class two years later. The University of Oregon is one of 60 members of the Association of American Universities. in Eugene. The researchers used a specially adapted atomic force microscope atomic force microscope (AFM), device that uses a spring-mounted probe to image individual atoms on the surface of a material. Unlike the scanning tunneling microscope, which is also a scanning probe microscope, the AFM can be used on materials that do not conduct to capture the interaction between a strand of DNA and an enzyme known as RNA polymerase, obtained in this case from the bacterium Escherichia coli. The polymerase initially binds to a DNA strand anywhere along its length, then slides like a bead on a string to find the sequence where it can start the transcription process. Snagging chemical building blocks known as nucleoside triphosphates (NTPs) from the surrounding liquid, the polymerase molecule reads DNA sequences to construct shorter strands called messenger RNA. In a subsequent step, the cell uses the information encoded in messenger RNA to produce a protein. To image RNA polymerase bound to DNA, Thomson and his colleagues measured minuscule deflections of the sharp tip of a stylus as it moved back and forth across molecules pinned to a mica surface. The entire assembly was bathed in a solution containing, at the start of the experiment, all but one of the ingredients essential for transcription. The polymerase began transcription but halted shortly thereafter, when it needed the missing building block. This pause allowed the researchers to focus on a single DNA-enzyme assemblage. "We're actually imaging while we're flowing liquid through the system," Thomson says. "In this way, we can initiate a change by adding the appropriate chemical." When the researchers introduced the final ingredient, transcription resumed and they observed the rest of the process. |
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