Abstract
While DNA may be viewed as the blueprint for the body, and mRNA/protein the component parts made from this blueprint, it is only when proteins are allowed to interact with each other and their surroundings that true biological complexity is achieved. Thus, while it is informative to study transcriptional control and mRNA transcript levels it is important to take this into the context of the total environment the encoded proteins are expressed in and how they interact with each other. At the very simplest level, expression of a ligand-activated receptor is of no biological consequence if the ligand is never present in the system, or the target for the activated receptor expressed in that cell type. It is thus important to be able to study these interactions to enable a comprehensive understanding of the biological interactions that underlying any particular phenotype. This article will outline the basic technologies to both visualise protein localisation and interaction between co-localised proteins. In addition, the manipulation of protein levels, both in vitro and in vivo, will be described, as this provides an important tool for the further examination of protein functionality within biological systems. © 2009 Elsevier Ltd. All rights reserved.