Targeting of Proteins to the Nucleus

This chapter discusses the targeting of proteins to the nucleus. Nuclear processes are involved in all aspects of plant cell growth and development. Understanding how proteins and nucleic acids are routed into and out of the nucleus is therefore of central importance to understanding how plant cells are regulated. The nucleus is a complex organelle enclosed by a double-membrane system through which macromolecular traffic must flow. Protein translocation into the nucleus, unlike other organelles, does not require the traversal of the lipid bilayers. The pores are composed of two stacked coaxial rings, each composed of eight subassemblies arranged symmetrically around a central plug. Although the diffusion exclusion limit of the pore is relatively high, permitting the passage of macromolecules of up to 60 kDa, transport of physiologically relevant proteins is dependent on cytosolic and pore-associated receptors that interact with one or more nuclear localization signals (NLSs) within the translocated protein.