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Chromatin Remodeling Rates

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Science's STKE  11 Sep 2001:
Vol. 2001, Issue 99, pp. tw325
DOI: 10.1126/stke.2001.99.tw325

The histone acetyltransferases are important for modification of chromatin to allow transcriptional activation of genes. In yeast, the PHO5 and PHO8 genes encode acid and alkaline phosphatases, respectively, and show enhanced transcription when concentrations of phosphate in the environment are decreased. Increased steady-state amounts of PHO8 produced in a low-phosphate environment require the activity of the histone acetyltransferase Gcn5, whereas expression of maximal amounts of PHO5 did not require Gcn5. However, when Barbaric et al. looked more closely at expression of PHO5, they found that although the extent of activation was the same regardless of the presence or absence of Gcn5, the rate of increase in transcription of PHO5 (but not that of other genes) was slower in cells lacking Gcn5. This effect appears to be mediated by chromatin remodeling and the consequent altered structure of the promoter, because the same effect was evident even when the PHO5 promoter was artificially modified to be regulated through the Gal4 activator. Thus, Gcn5 shows two modes of regulation--one in which the activity is absolutely required for transcriptional activation, and another in which only the rate of chromatin remodeling is altered. The authors caution that measures of steady-state expression of regulated genes may fail to reveal biologically important differences in the rate of gene expression brought about by chromatin remodeling enzymes like Gcn5.

S. Barbaric, J. Walker, A. Schmid, J. Q. Svejstrup, W. Hörz, Increasing the rate of chromatin remodeling and gene activation--a novel role for the histone acetyltransferase Gcn5. EMBO J. 20, 4944-4951 (2001). [Abstract] [Full Text]

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