Dear Editor,
The conformation of nucleosomal DNA is significantly different from that of B-form double stranded DNA (dsDNA) (Richmond and Davey, 2003). In nucleosomal DNA, specific DNA sequences are less flexible and less accessible than in free dsDNA, which might be due to the tight association of histone cores. The allosteric effect via DNA has been documented recently (Kim et al., 2013), suggesting that DNA is not merely a solid rod providing recognition sequences. Previous studies of nucleosomal DNA–protein interactions only demonstrated the key mechanism involved—histone shielding (Li and Wrange, 1993; Hinz et al., 2010; Sahu et al., 2010). How conformational changes in nucleosomal DNA, compared with free dsDNA, affect nucleosomal DNA–protein interactions remains unknown.