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Scientists discover new rules about 'runaway' transcription

On the evolutionary tree, humans diverged from yeast roughly 1 billion years ago. By comparison, two seemingly similar species of bacteria, Escherichia coli and Bacillus subtilis, have been evolving apart for roughly twice as long. In other words, walking, talking bipeds are closer on the tree of life to single-celled fungi than these two bacteria are to one another. In fact, it's becoming increasingly clear that what is true of one bacterial type may not be true of another—even when it comes down to life's most basic biological pathways.

E. coli has served as a model organism in scientific research for over a century, and helped researchers parse many fundamental processes, including gene expression. In these bacteria, as one molecular machine, the RNA polymerase, moves along the DNA transcribing it into RNA, it is followed in close pursuit by a second molecular machine, the ribosome, which translates the RNA into proteins. This "coupled" transcription-translation helps monitor and tune RNA output, and is considered a hallmark of bacteria.

However, an interdisciplinary team of biologists and physicists recently showed that the B. subtilis bacterium employs a different set of rules. Rather than working in tandem with the ribosome, the polymerase in B. subtilis speeds ahead. This system of "runaway" transcription creates alternative rules for RNA quality control, and provides insights into the sheer diversity of bacterial species.

"Generations of researchers, including myself, were taught that coupled transcription-translation is fundamental to bacterial gene expression," says Gene-Wei Li, an associate professor of biology and senior author of the study. "But our very precise, quantitative measurements have overturned that long-held view, and this study could be just the tip of the iceberg."

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