Back to units of protein folding.

In response to the criticism by A. Finkelstein (J Biomol Struct Dyn 20, 311-314, 2002) of our Communication (J Biomol Struct Dyn 20, 5-6, 2002) several issues are dealt with. Importance of the notion of elementary folding unit, its size and structure, and the necessity of further characterization of the units for the elucidation of the protein folding in vivo are discussed. The criticism (J Biomol Struct Dyn 20, 311-314, 2002) on the hierarchical protein folding is also briefly addressed.