RNA chaperone activity of DEAD‐box ‘helicase’ proteins

Abstract

Cellular RNAs are able to fold to specific functional structures and carry out a host of critical processes despite an inherent propensity of RNA to fold to alternative conformations. In vivo, RNA misfolding is mitigated by RNA chaperones, notably DEAD‐box ‘helicase’ proteins. CYT‐19 is a Neurospora crassa DEAD‐box protein that chaperones folding of several mitochondrial group I introns. To probe the mechanisms of RNA chaperone activity, we have dissected CYT‐19‐promoted folding of the well‐studied Tetrahymena group I intron ribozyme. This ribozyme misfolds to a long‐lived intermediate, and the DEAD‐box chaperone protein CYT‐19 accelerates its folding to the native state by using ATP to promote RNA unfolding non‐specifically. This unfolding allows loss of the non‐native structure and a second chance for the RNA to fold correctly. Although CYT‐19 and other DEAD‐box proteins possess limited helicase activity, their substrate RNAs are globular and include extensive tertiary structure, and it is not clear how unfolding of complex RNA structures is achieved. I will describe recent single molecule fluorescence and biochemical experiments that probe directly whether CYT‐19 can use ATP‐dependent RNA binding and unwinding activities to disrupt tertiary contacts within the intron. The results have implications for how DEAD‐box proteins chaperone RNA folding processes.