New study finds previous textbook descriptions of the gene transcription process were wrong. Using advanced cryo-electron microscopy techniques, a new study has for the first time seen part of the process of gene transcription in a cell.
Gene transcription is the essential foundation of almost all life, with messenger RNA acquiring instructions within genes and directing cells to do their designated jobs. Scientists previously understood the process of transcription as follows: RNA uses polymerase to wrap around the double-linked construct of DNA and begin copying the information encoded in one of the strands. When the information is copied, a mechanism separates the RNA from the DNA strand, and the transcription process is complete.
This process is controlled by a Rho protein. For more than fifty years since its discovery, textbooks have used this protein as a typical stop-transcription protein, believing that it would automatically bind to the RNA when transcription was complete and pull the transcribed RNA out of the polymerase structure wrapped around the DNA.
However, the new study finds that it is impossible for Rho to find and bind to the RNA and pull it out at the end of transcription, but rather it remains inside the RNA polymerase, and at the end of transcription, in cooperation with other proteins, changes the structure of the large polymerase wrapped around the outside of the DNA, causing it to release the RNA that has completed its replication work.
The study, which used E. coli as its subject, is the first time scientists have photographed the inner RNA polymerase at work. This is the first transcriptional termination structure (observed) in any system,” said Irina Artsimovitch, one of the study’s authors and a professor of microbiology at Ohio State University in the United States. In the presence of the protein Rho, the process of changing the structure of the polymerase occurs quite rapidly, if not within seconds, then within minutes. We were unable to extract a stable polymerase structure for analysis, but we were able to observe the process.”
Previous textbooks on the working mechanism of the protein Rho were based on simplified biochemical experiments that largely ignored the crude process defined by the most critical element of the process, the RNA polymerase, Alcimovic said.
This study used cryo-electron microscopy to capture the RNA polymerase structure within E. coli DNA and combined it with computer analysis to understand the precise transcriptional termination process.
The study was published Nov. 26 in the journal Science.
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