Unstressed cells (Image 1 of 2). Immunofluorescent light micrograph of unstressed kidney cells. The nuclei contain the RNA (ribonucleic acid)-binding protein TIA (blue) and DNA (deoxyribonucleic acid) storage proteins (histones, green). The addition of acetyl groups (acetylation) to the amino acid lysine, which is found in histones, causes the DNA to become less tightly bound to the histones, resulting in the production (transcription) of proteins. Acetylation can also occur in the structural protein tubulin but can usually only be detected at the end of cell division (green, top right). Also present is the new protein FAST K (red). For stressed cells, see P551/007.