Why can chaperone proteins help in an expression host?

Correct answer: To help protein folding

The governing concept is assisted folding of recombinant proteins. Chaperone proteins are cellular factors that bind newly synthesized or partially folded polypeptides and help them reach an appropriate three-dimensional conformation. In an expression host producing a foreign protein at high levels, folding machinery may become limiting, causing aggregation or insoluble inclusion bodies. Extra or co-expressed chaperones can sometimes increase the fraction of correctly folded, soluble product, although their effect depends on the protein and conditions. Thus A is correct; the other options describe DNA entry, water production, or DNA cleavage, none of which is the primary role of chaperones.