Isolation of differentially expressed genes by cloning transcriptionally active DNA fragments

During studies of erythroid cell growth and differentiation induced by eryt hropoietin (Epo), we developed a method that allows the identification and isolation of genes based upon their transcriptional activity. Transcription ally active genomic DNA fragments from Epo-treated cells and control cells are purified from inactive chromatin using mercury affinity chromatography, based on the mechanism that the thiol groups of histone H3 on transcriptio nally active chromatin are exposed to the solvent and therefore are easily accessible. Using the purified genomic DNA fragments from the two populatio ns of cells, a subtractive hybridization strategy is used to isolate and cl one genes that are differentially expressed in the absence or in the presen ce of Epo. (C) 1999 Academic Press.