Protein targeting to subnuclear higher order structures: a new level of regulation and coordination of nuclear...

Though there are no separating membranes within the nucleus, different factors are often concentrated at sites where their respective function is required, a phenomenon referred to as functional organization of the nucleus. How is then this organization achieved and how are the different metabolic processes integrated in the nucleus? One emerging principle was revealed by the identification of protein domains that, though not involved in catalysis, regulate enzyme activity at a higher order level by targeting enzymes to the right place at the right time. These targeting sequences constitute an assembly code for nuclear 'protein factories,' which ensure the extremely high efficiency and accuracy needed in a complex and competitive environment as the living mammalian cell.