Cell Biology

As It Happens

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Science  13 Nov 2009:
Vol. 326, Issue 5955, pp. 917
DOI: 10.1126/science.326.5955.917-d

RNA polymerase moves information from the genome (DNA) into pre-messenger RNA (pre-mRNA), from which introns are removed and exons are ligated to make a mature mRNA. To follow the progress of transcription on single genes from start to finish, Wada et al. chose five long human genes whose expression could be switched on by the cytokine tumor necrosis factor–α. Putting together snapshots taken at 7.5-min intervals for 3 hours, they documented the waves of RNA synthesized by polymerase, with each molecule of enzyme jumping on at the transcription start site and hopping off over 100 kb away. During each round, upstream introns were excised as the polymerase moved downstream, often before the next intron was reached. Furthermore, it appeared that later rounds of transcription were begun and continued for a few kilobases before being aborted, as if the polymerases were colliding with a checkpoint that kept track of downstream occupancy of the gene. Each wave of transcription traveled at ∼3 kb m−1, although the accumulation of polymerase at regions bound by the insulator proteins CTCF and cohesion, both of which are involved in chromosome looping, suggested that polymerase may be held up at specific sites.

Proc. Natl. Acad. Sci. U.S.A. 106, 18357 (2009).

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