Chromatin-bound cardiolipin: the phospholipid of proliferation.

Chromatin-bound lipids, cardiolipin (CL), diglycerides, cholesterol, and cholesterol esters, together with nonhistone proteins, play a key role in structural and functional organization of the chromatin genome during various stages of evolution. There are two pools of chromatin lipids, namely loosely- and tightly-bound lipids. The entire chromatin cardiolipin is bound to DNA. The CL molecule has a common 'interphosphate' structural motive with DNA, i.e. DNA and CL phosphate moieties separated from each other with six chemical bonds and equidistant, which is important for CL functional role, the regulation of gene expression. The CL dominates in the DNA of the active genome but not in the DNA of the repressed genome. The amount of CL in the DNA from the repressed genome of pigeon erythrocytes (one CL molecule per 20 nucleosomes) is 20 times less than in the DNA from the active genome of rat thymus and liver and in the DNA of transformed cells. Cardiolipin provides A-form DNA in the complex with RNA-polymerase, which is necessary for transcription. The biological and structural function of cardiolipin can be realised only when unsaturated fatty acyl residues are present in its structure.