Alert to biologists: Ribosomes can translate the untranslated region of messenger RNA

In what appears to be an unexpected challenge to a long-accepted fact of biology, Johns Hopkins researchers say they have found that ribosomes - the molecular machines in all cells that build proteins - can sometimes do so even within the so-called untranslated regions of the ribbons of genetic material known as messenger RNA (mRNA).

"This is an exciting find that generates a whole new set of questions for researchers," says Rachel Green, Ph.D., a Howard Hughes Medical Institute investigator and professor of molecular biology and genetics at the Johns Hopkins University School of Medicine. Chief among them, she adds, is whether the proteins made in this unusual way have useful or damaging functions and under what conditions, questions that have the potential to further our understanding of cancer cell growth and how cells respond to stress.

In a summary of the findings in yeast cells, to be published Aug. 13 in the journal Cell, Green and her team report that the atypical protein-making happens when ribosomes fail to get "recycled" when they reach the "stop" signal in the mRNA. For reasons not yet understood, Green says, "rogue" ribosomes restart without a "start" signal and make small proteins whose functions are unknown.