An 'immune system' embedded in Escherichia coli's genome protects the bacterium against injurious genes acquired from other organisms.
A protein called Rho helps E. coli produce some RNA molecules because it indicates when to stop making them. Evgeny Nudler of New York University School of Medicine, Max Gottesman of Columbia University Medical Center, New York, and their team exposed E. coli to an antibiotic called bicyclomycin that inhibits Rho. Without this stop signal, many genes that viruses and other bacterial species have transferred into the E. coli genome were newly expressed, often with toxic effects.
One such gene, acquired from a virus, inhibits cell division. Taken together, the findings suggest that Rho blocks the expression of harmful foreign genes.