Neurospora crassa and S1 nuclease cleavage in hsp 83 gene chromatin.

We have examined the distribution of Neurospora crassa and S1 nuclease cleavage products in the chromatin of the hsp 83 heat shock gene from the Drosophila melanogaster cytogenetic locus 63 BC. Both of these nucleases generate double strand breaks in chromatin at specific sites close to the 5' end of the hsp 83 gene. With N. crassa nuclease we observe one major 5' fragment which is derived from nuclease cleavage in a DNA segment mapping approximately 120 base-pairs from the beginning of the transcription unit. With S1 nuclease we observe one major fragment which overlaps the transcription start site. In addition to the major hypersensitive sites at the beginning of the gene, the hsp 83 transcription unit is also sensitive to attack by these nucleases both before and after heat shock; however, the yield of cleavage products from within the gene is considerably greater after heat induction.