Though in vitro protein folding studies have produced insight into mechanisms underlying protein folding and energy landscapes, we do not completely understand how cellular factors modulate folding. All proteins have the opportunity to fold when synthesized from N- to C-terminus by the ribosome, which builds polypeptide chains at a rate of about 10 residues per second. This is much slower than the average folding rate of most small proteins, giving the nascent chain time to sample different conformations throughout translation.