R-loop

<p>An R-loop is a three-stranded nucleic acid structure, composed of a DNA:<a href="/facts/RNA/HxPeNfNj">RNA</a> hybrid and the associated non-template single-stranded <a href="/facts/DNA/nB89Iauz">DNA</a>. R-loops may be formed in a variety of circumstances and may be tolerated or cleared by cellular components.  The term "R-loop" was given to reflect the similarity of these structures to <a href="/facts/D-loop/4yt3q9n9">D-loops</a>; the "R" in this case represents the involvement of an RNA <a href="/facts/Moiety_(chemistry)/WxKqcJe1">moiety</a>.
</p><p>In the laboratory, R-loops can be created by transcription of DNA sequences (for example those that have a high GC content) that favor annealing of the RNA behind the progressing RNA polymerase. At least 100bp of DNA:RNA hybrid is required to form a stable R-loop structure. R-loops may also be created by the <a href="/facts/Nucleic_acid_hybridization/j77KBWPJ">hybridization</a> of mature mRNA with double-stranded DNA under conditions favoring the formation of a DNA-RNA hybrid; in this case, the <a href="/facts/Intron/LS6YdBEK">intron</a> regions (which have been <a href="/facts/Splicing_(genetics)/a2QEvCRI">spliced</a> out of the mRNA) form single-stranded DNA loops, as they cannot hybridize with complementary sequence in the mRNA. 
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R-loop open-in-new

R-loop