A newly identified protein complex allows cells to vary the rate at which they make ribosomes — the factories that translate RNA into protein — in response to how much energy is available. Ribosome production is the most energetically expensive thing that eukaryotic cells do, so the complex has an important role in cell survival.
A team led by Junn Yanagisawa of the University of Tsukuba in Japan isolated a protein complex called NoSC that controls transcription of ribosomal RNA, the main component of ribosomes, in response to the ratio of NAD+ to NADH molecules, a signal of the available energy in a cell. NoSC contains a previously uncharacterized protein, named nucleomethylin, that binds one of the histone proteins with which DNA is packaged. It also comprises SIRT1, a protein made in response to caloric restriction and SUV39H1, which can alter gene expression.