Proteins that control gene expression by attaching to specific DNA sequences amble along chromosomes until they hit their targets, according to a single-molecule imaging study.

In the 1970s, researchers theorized that one such protein, or transcription factor, called the lac repressor (LacI) would act in this way. Johan Elf and his team at Uppsala University in Sweden provide the first evidence of this behaviour in vivo. In Escherichia coli cells, the team found that LacI took 3–5 minutes to bind to the correct DNA site — the speed predicted by theoretical models of 'chromosome crawling'. When other proteins are bound to the chromosome, they act like roadblocks and slow the search. Moreover, the transcription factor typically slides over its target several times before binding to it.

Science 336, 1595–1598 (2012)