In the April 1 issue of Genes & Development, a Korean research team led by Dr. Kyong-Tai Kim (Pohang University) describes how melatonin production is coordinated with the body's natural sleep/wake cycles.
Melatonin is a hormone produced by the pineal gland in the brain, which helps to regulate our bodies' circadian rhythm (the roughly-24-hour cycle around which basic physiological processes proceed). Normally, melatonin production is inhibited by light and enhanced by darkness, usually peaking in the middle of the night. Melatonin's expression pattern is mimicked by a protein called AANAT, which is a key enzyme in the melatonin biosynthesis pathway.
Dr. Kim and colleagues uncovered the mechanism of rhythmic control of AANAT mRNA translation, and thereby melatonin synthesis. The researchers found that rodent AANAT mRNA translation is mediated by IRES (internal ribosome entry site) elements in the 5' end of the transcript, through binding of another protein, called hnRNP Q. In fact, siRNA knock-down of hnRNP Q reduced AANAT and melatonin production under nocturnal conditions.