Editing DNA (section)

=== Grooves ===
[[File:DNA-ligand-by-Abalone.png|thumb|DNA major and minor grooves. The latter is a binding site for the [[Hoechst stain]] dye 33258.]]

Twin helical strands form the DNA backbone. Another double helix may be found tracing the spaces, or grooves, between the strands. These voids are adjacent to the base pairs and may provide a [[binding site]]. As the strands are not symmetrically located with respect to each other, the grooves are unequally sized. The major groove is {{convert|22|Å|nm}} wide, while the minor groove is {{cvt|12|Å|nm}} in width.<ref>{{cite journal | vauthors = Wing R, Drew H, Takano T, Broka C, Tanaka S, Itakura K, Dickerson RE | title = Crystal structure analysis of a complete turn of B-DNA | journal = Nature | volume = 287 | issue = 5784 | pages = 755–58 | date = October 1980 | pmid = 7432492 | doi = 10.1038/287755a0 | bibcode = 1980Natur.287..755W | s2cid = 4315465 }}</ref> Due to the larger width of the major groove, the edges of the bases are more accessible in the major groove than in the minor groove. As a result, proteins such as [[transcription factor]]s that can bind to specific sequences in double-stranded DNA usually make contact with the sides of the bases exposed in the major groove.<ref name="Pabo1984">{{cite journal | vauthors = Pabo CO, Sauer RT | title = Protein-DNA recognition | journal = Annual Review of Biochemistry | volume = 53 | pages = 293–321 | year = 1984 | pmid = 6236744 | doi = 10.1146/annurev.bi.53.070184.001453 }}</ref> This situation varies in unusual conformations of DNA within the cell ''(see below)'', but the major and minor grooves are always named to reflect the differences in width that would be seen if the DNA was twisted back into the ordinary [[B-DNA|B form]].