Demonstration of an S1-nuclease sensitive site near the human beta-globin gene, and its protection by HMG 1 and 2.

An S1-nuclease sensitive site exists within supercoiled plasmids containing the 5'-flanking sequences of the human beta-globin gene. This site is located approximately 540 base pairs upstream from the start of the gene within a region of 52 alternating purine-pyrimidine residues which has the potential to adopt either cruciform structures or Z-form DNA. This site is protected from specific cleavage by S1-nuclease by the high-mobility-group chromosomal proteins HMG1 and 2, which may be specifically acting to protect short sequences of single-stranded DNA.