Mapping of mouse 5′ HS 6. The same wild-type 129-mouse erythroid DNase I series displayed in Fig 2 was digested withXba I (X), Southern blotted, and hybridized with a probe on the 5′ end. Molecular size standards are marked on the left. The “0” lane shows the expected parent band in untreated nuclei followed by samples having undergone increasing DNase I digestion. The expected 6.9-kb parent band and a degradation band that maps to −28.4 kb (in parentheses), which we refer to as 5′ HS 6 (see text), are observed. The size of the parent band, placement of the probe used (KH end), and the size of the degradation band are diagrammed below.Xba I cuts at −27,346 and −34,263 relative to the Ey cap. Mapping of the site was confirmed by hybridizing with a probe from the 3′ end of the same restriction fragment as well as mapping with additional restriction enzymes (data not shown).