THE BULK CHROMATIN STRUCTURE OF A MURINE TRANSGENE DOES NOT VARY WITHITS TRANSCRIPTIONAL OR DNA METHYLATION STATUS

The DNA methylation status of HRD, a murine transgene, can be controll ed by the genetic background upon which it is carried. We found the tr ansgene to be transcribed in competent tissues only when undermethylat ed. Chromatin structure over the transgene was assayed by nuclear acce ssibility with DNase I, MspI, and PstI. While the transgene was up to fivefold more resistant to MspI when methylated than when not methylat ed, we observed no such difference with DNase I or PstI. We suggest th at methyl-CpG-binding proteins are responsible for the difference obse rved with MspI, but that the chromatin structures are otherwise simila rly compacted. Methylation could, therefore, play a regulatory role in gene expression beyond that which can be accomplished by bulk chromat in structure alone.