Proteome and phosphoproteome analysis of chromatin associated proteins in rice (Oryza sativa)

The eukaryotic chromatin/chromosome stores genomic information, controls genetic material distribution, and plays an essential role in the establishment and maintenance of spatial and temporal gene expression profile. Despite over a century of research, the protein composition and higher level structure of chromatin still remain obscure, particularly in plants. In this report, we have developed a protocol for chromatin purification from rice suspension cells and examined proteins copurified with chromatin using both 2-DE gel and shotgun approaches. Nine hundred seventy-two distinct protein spots have been resolved on 2-DE gels and 509 proteins have been identified by MALDI-MS/MS following gel excision, which correspond to 269 unique proteins. When the chromatin copurified proteins are examined using shotgun method, a large number of histone variants in addition to the four common core histones have been identified. Other proteins identified include nucleosome assembly proteins, high mobility group proteins, histone modification proteins, transcription factors, and a large number of hypothetical and function unknown proteins. Furthermore, putative phosphoproteins copurified with chromatin have been examined using Pro-Q Diamond phosphoprotein stain and followed by MALDI-MS/MS. Our studies have provided valued new insight into chromatin composition in plants.