Is there specific transcription from isolated chromatin?
Hg-UMP-containing transcripts made from chick erythroid chromatins with E. coli RNA polymerase hybridize to chick globin cDNA. Contamination with endogenous globin RNA has been largely removed by purification on SH-agarose columns at 55°C. Some endogenous globin mRNA sequences remain, probably as hybrids with “anti-sense” Hg-transcripts produced by RNA-dependent RNA synthesis. Heating to 115°C before SH-agarose chromatography eliminates these contaminants. Hg-transcripts from adult and embryonic erythroid chromatins purified by this method are hybridized to globin cDNA; they contain a 4- to 6-fold higher proportion of globin-specific sequences (10–13 ppm) than do transcripts from brain chromatin. Dissociation of erythroid chromatins in salt and urea, followed by reconstitution using standard methods, destroys even this low degree of specificity.
