A generic term for any member of a large class of proteins associated with nucleic acid molecules. Nucleoprotein complexes occur in all living cells and viruses, where they play vital roles in deoxyribonucleic acid (DNA) replication, transcription, ribonucleic acid (RNA) processing, and protein synthesis. The chemistry of the nucleoproteins has become one of the fastest-growing areas in cell and molecular biology. Developments in this field have already revolutionized our understanding of complex biological processes within a cell. These advances will have important consequences in the treatment of genetic disease, viral infections, and cancer.