Gourse's group found that there is a specific region within DNA promoters that makes contact with a highly conserved but previously underappreciated segment of the sigma subunit of RNA polymerase. While the contact with sigma is very strong at promoters for most genes, it is particularly weak at promoters that make ribosomal RNA, which means that other factors like nutritional and environmental signals ultimately regulate the expression of those genes.
"In this case, regulation is achieved not because the promoter makes a special contact, but because it can't establish contact at all," says Gourse. "This is an example of how sometimes less is more, and a probably very ancient example of one of the methods that arose through evolution to regulate gene expression."
Ribosomal RNA makes up the bulk of ribosomes, the molecular machines that make proteins and are present in huge numbers in all cells. Since so much of the cell's energy is used to make ribosomes, control of ribosomal RNA transcription is particularly crucial to a cell's well-being.
"This work is basic to the growth of all bacteria," says Gourse. "By understanding transcription and control of ribosome synthesis in E. coli, we can understand more about these processes in bacterial species that we need to control, like those that cause disease or make toxins. E. coli is also the workhorse of the biotechnology industry. Understanding E. coli gene expression in detail allows us to harness these cells for producing products of biotechnological importance, like pharmaceuticals."
Gourse's work was supported by the National Institutes of Health, the United States Department of Agriculture, and by Pfizer Biotechno
Source:University of Wisconsin-Madison