How DNA forms human proteins can be followed in real time

London: The study of the real-time dynamics of gene expression may help to explain variation among genetically identical cells and the molecular processes that lead to cancer, say researchers.

The researchers created two clones of a human embryonic kidney cell line with an engineered version of the gene cyclin D1, which controls the cell cycle.

Both clones included a DNA sequence that allows a fluorescent protein expressed in the cell to bind to cyclin D1 RNA the moment it is transcribed. One clone depended on the gene’s natural promoter - the binding site for the polymerase enzyme that transcribes DNA into mRNA - whereas the other was fused to a viral promoter known to over express genes by producing an abundance of mRNA.

By visualizing the process at the level of a single gene, the researchers were able to work out the different mechanics of transcription between the human and viral promoter.

The cells with the normal promoter shut down for about 20 minutes every 200 minutes, whereas the cells with the viral promoter remained active for a 10-hour stretch.

More significantly, the latter group of cells recruited twice as many polymerase enzymes - about 14 - which crammed along the gene’s length, all producing mRNA.

"In our system, the cell line has a target sequence in its genome and any sequence you send in will always go to that place," Nature quoted Yaron Shav-Tal, of Bar-Ilan University, as saying.

"You can make different cell lines and not be worried about where the gene went in," he said.

The method will allow researchers to investigate the mechanics of other promoters, as well as disparate phenomena such as the pulsing of hormones produced by the endocrine system.

"This is a whole new outlook," said Tav-Shal.

"People now know that even if the whole population of cells is supposed to be identical, each one has a different expression profile," he added.


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