Chromatin structure of hsp 70 genes, activated by heat shock: selective removal of histones from the coding region and their absence from the 5' region.

The presence of histones in hsp 70 genes was studied by "protein-image" hybridization technique after crosslinking histones to DNA. With increasing transcription of the genes, the coding region was demonstrated to be depleted first of H1 and then of all histones. This probably accounts for unraveling the 25 nm silent chromatin fiber to moderately and actively transcribed 10 nm fiber and linearized DNA. No histones were found in the 5'-terminal DNAase I-hypersensitive region, which may be a prerequisite to gene activation. The absence of histones on DNA correlates well with the high nuclease sensitivity and disappearance of the regular pattern in micrococcal nuclease digests of chromatin.