Various sequence blocks. due to their specific primary sequence box, and/or a curved helical DNA conformation. and/or a non-β-helical DNA structure, can be organized in the corresponding higher order structures and behave as functional sequence domains recognized and bound by specific proteins. They may be defined as “code domains”. Code domains are genetically instructive for specific molecular interactions or processes, important not only in nucleus during interphase and during cell division but also in diferential gene expression during development and differentiation.