Transcription factors (TFs) are proteins that regulate the expression of
genes by binding sequence-specific sites on the chromosome.
It has been proposed that to find these sites
fast and accurately, TFs combine one-dimensional (1D) sliding on DNA
with 3D
diffusion in the cytoplasm. This facilitated
diffusion mechanism has been demonstrated in vitro, but it has not been
shown
experimentally to be exploited in living cells.
We have developed a single-molecule assay that allows us to investigate
the
sliding process in living bacteria. Here we show
that the lac repressor slides 45 ± 10 base pairs on chromosomal DNA and that sliding can be obstructed by other DNA-bound proteins near
the operator. Furthermore, the repressor frequently (>90%) slides over its natural lacO1 operator several times before binding. This suggests a trade-off between rapid search on nonspecific sequences and fast binding
at the specific sequence.
http://www.sciencemag.org/content/336/6088/1595.full
Friday, June 22, 2012
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