Identification and characterization of nonhistone chromatin proteins: human positive coactivator 4 as a candidate

The highly dynamic nucleoprotein structure of eukaryotic genome is organized in an ordered fashion, the unit of which is the nucleosome. The nucleosome is composed of core histones and DNA of variable size wrapped around it. Apart from the histone proteins, several nonhistone proteins also interact with the complex consisting of the DNA, the core and linker histones conferring highly regulated fluidity on the chromatin and permitting fine tuning of its functions. The nonhistone proteins are multifunctional and accentuate diverse cellular outcomes. In spite of the technical challenges, the architectural role of the nonhistone proteins altering the topology of the chromatin has been studied extensively. To appreciate the significance of the chromatin for genome function, it is essential to examine the role of the nonhistone proteins in different physiological conditions. Here, taking the example of a highly abundant chromatin protein, PC4 (Positive coactivator 4), we describe strategies for the identification of the chromatin-associated proteins and their structural and functional characterization.