One by one: Molecular biology 22/8/06. By the Wellcome Trust A US group has managed to develop methods to study production of single protein molecules.

Much of our understanding of cell biochemistry – such as how DNA is read into RNA and used as a template for protein production – has come from studies of populations of cells. With technological advances, though, it is becoming possible to watch events within an individual cell. Now, a Harvard research group led by Professor Sunney Xie has developed not one but two methods for observing the synthesis of individual proteins in living cells.

In one, the team produced a fluorescent reporter protein engineered to lodge itself in the bacterial cell membrane. Normally, such a protein inside the cell would diffuse around too quickly to be identified, but trapped in the membrane, each protein can be detected individually.

In a second paper, the Harvard group used the small volume of a microfluidic device containing a single bacterium to capture fluorescent product molecules that are generated from a single enzyme and pumped out of the cell.

The experiments confirm directly what in the past could only be assumed from bulk measurements: that while particular mRNA species have distinct average lifetimes, individual transcripts show considerable variability in lifespan. More generally, the methods open up the possibility of studies of fundamental processes such as gene activation and protein synthesis at the individual molecule level, and in a wide variety of cells.

References

Cai L et al. Stochastic protein expression in individual cells at the single molecule level . Nature 2006;440(7082):358–62.

Yu J et al. Probing gene expression in live cells, one protein molecule at a time . Science 2006;311(5767):1600–3.