By tagging the products from a single gene locus with green fluorescent protein (GFP), the kinetics of transcription can be followed in single cells, demonstrates work published online this week in Nature Methods.
The extent and timing of transcription ― where RNA copies of DNA sequences are made ― is tightly regulated and varies widely between genes. Current methods that target transcripts provide information on the average level of mRNA expression but cannot be used to investigate the speed or fluctuation of transcription.
By inserting a single copy of a gene, driven by a viral or its internal promoter and containing a docking site for GFP at the far side of the gene, Yaron Shav-Tal and colleagues monitor expression of this gene over time, count how many mRNA molecules are produced at the locus, and measure the speed of transcription. Comparing the kinetics of transcription from the viral and the internal promoter, the team observed considerable differences ― for example, that the former showed ongoing transcription whereas the latter was turned off during certain stages of cell division. Performing this kinetic analysis in real time on single loci in single cells will allow the detailed study of the regulation of gene transcription and its interplay with cell division.