Effect of protein binding on RNA folding

Large RNA molecules are typically associated with proteins, some of which bind early to direct folding of the RNA and some of which bind later to maintain the correct RNA fold. Specifically how these proteins participate in the RNA folding process is not clear, but most appear to direct tertiary structure after the RNA has formed its secondary structure. CYT-18 binding to group I introns and S4 and S15 binding to 16S rRNA are examples of these interactions. DEAD box helicases unwind short duplexes in a folded RNA to allow it to rearrange its tertiary structure; examples are the helicase DbpA, which functions specifically on 23S rRNA, and Cyt-19 helicase, which works on many group I introns. What is known about these systems is related to what is generally understood about how proteins function to fold RNA.