The distribution of somatic H1 subtypes is non-random on active vs. inactive chromatin: Distribution in human fetal fibroblasts

Chromatin immunoprecipitation was employed to determine whether or not the previously reported depletion of histone H1 on actively transcribed sequenc es was selective with respect to H1 subtypes. DNA of immunofractionated chr omatin was analyzed by slot-blots for repetitive sequences and PCR for sing le and low-copy sequences. Based on the analysis of a diverse set of sequen ces, we report distinct differences in subtype distributions. Actively tran scribed chromatin, as well as chromatin poised for transcription, is charac terized by a relative depletion of somatic H1 subtypes 2 and 4 (H1(s)-2 and H1(s)-4), whereas facultative and constitutive heterochromatin contain all four somatic subtypes. These results support a model in which subtypes are selectively depleted upon gene expression. In turn, the data also support the possibility that the somatic subtypes have different functional roles b ased on their selective depletion from different classes of DNA sequences.