FIG. 4.
Effect of A:T tract length and orientation of G:C base pairs on DNA methylation. (A) Long A:T tracts are not required to trigger methylation. The 100-mer sequences related to the best methylation signal identified, (TAAA)n (see Fig. 2B), were constructed and tested as methylation signals at the amRIP4::ζ−η100 test site. Note that sequences 1 and 2 have 5-bp A:T tracts, sequences 3 and 4 have 4-bp A:T tracts, sequences 5 and 6 have 3-bp A:T tracts, and sequences 7 to 10 have 2-bp A:T tracts. (B) Effect of orientation of G:C pairs on de novo methylation at the amRIP4::ζ−η100 test site. Pairs of similar sequences (2 and 3, 4 and 5, 7 and 8, and 9 and 10) that differ only in the orientation of the single G:C in the repeat unit were tested as described for Fig. 2. Inserts 1 and 6 are control test sequences that have neither TpA nor ApT dinucleotides.