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Comment
. 2011 Jun 24;332(6037):1510-1.
doi: 10.1126/science.1208450.

Molecular biology. A new twist for topoisomerase

Susana M Cerritelli  1 , Hyongi Chon, Robert J Crouch
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Comment

Molecular biology. A new twist for topoisomerase

Susana M Cerritelli et al. Science. .
No abstract available

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Figures

Figure
Figure
On top. (A) In yeast wild-type cells (TOP1, RNase H2), R-loop formation is prevented when Top2 relieves the positive supercoiling ahead of the transcribing RNA polumerase, and Top1 relieves the negative supercoiling behind. RNase H2 cleaves rNMPs incorporated into DNA, which leads to their replacement with dNMP. (B) In top1Δ mutants, RNA/DNA hybrids are formed and processed by RNase H1/H2, and rNMP removal is initiated by RNase H2. Mutations can result by TAM and TAR. (C) in rnh2Δ cells, Top1 will encounter and cleave rNMPs that have not been removed because RNase H2 is missing, which produces 2- to 5-bp deletions. (D) In the double mutant top1Δ rnh2Δ, RNA in R-loops may be cleaved by RNase H1, but rNMPs will remain in the DNA. DNA is blue, RNA is red, and single rNMPs in DNA are noted as red R.
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