Proteins, RNAs and chaperones in enzyme evolution: a folding perspective

The present roles of RNA molecules as templates and of proteins as cellular catalysts may not have always been so clearly defined during evolution. Recent work on ribozymes shows that the catalytic activity of early RNAs may have been more general than previously thought. How did evolution select proteins, not RNA, to be the major biological catalysts? Why were chaperones necessary for the evolution of modern protein enzymes?