Nature Chem. Biol. doi:10.1038/nchembio.138 (2009)

New fluorescent 'timers' that gradually change colour from blue to red could allow researchers to track the age and dynamic behaviour of proteins in living cells.

Previous work suggested that some red fluorescent proteins start out fluorescing blue, but then change to red as the protein is chemically modified over time. Vladislav Verkhusha and his colleagues at the Albert Einstein College of Medicine in New York mutated a red fluorescent protein called mCherry, then screened for mutants that had altered maturation rates from blue to red.

The researchers developed three fluorescent proteins, each with a specific maturation rate. The proteins were used to track newly synthesized proteins in mammalian cells grown in culture.