Nuclease-hypersensitive sites in the chromatin domain of the chicken lysozyme gene.

We have examined the chromatin structure of a 22 kilobase-pair chromosomal region containing the lysozyme gene in laying hen. Nuclease-hypersensitive sites were probed with DNAase I by using an indirect end-labeling technique. Eight DNAase I-hypersensitive sites could be mapped in the flanking regions of the gene in oviduct cells, in which the gene is expressed. The same sensitive sites were detected by utilization of an endogenous nuclease activity present in oviduct nuclei. Only one hypersensitive site was detected in the chromatin from erythrocytes, in which the gene is not expressed. The 3'-terminus of the lysozyme gene is highly exposed in nuclei from both tissues. Of special interest is the hypersensitive site at the 5'-terminus of the actively transcribed gene since it maps at the region of multiple initiation sites of transcription and the putative control regions of steroid hormones. DNAase I-hypersensitive chromatin structures also at a greater distance from the gene may take part in the control of gene expression.