Human immunoglobulin kappa gene enhancer: chromatin structure analysis at high resolution.

The murine immunoglobulin kappa gene enhancer has previously been found to coincide with a region of altered chromatin structure reflected in a DNase I hypersensitivity site detectable on Southern blots of B-cell DNA. We examined the chromatin structure of the homologous region of human DNA using the high-resolution electroblotting method originally developed for genomic sequence analysis by G. Church and W. Gilbert (Proc. Natl. Acad. Sci. USA 81:1991-1995, 1984). Analysis of DNA isolated from cells treated in vivo with dimethyl sulfate revealed two B-cell-specific sites of enhanced guanine methylation. Both sites are located within perfect inverted repeats theoretically capable of forming cruciform structures; one of these repeats overlaps an enhancer core sequence. No enhancement or protection of guanine methylation was observed within sequences similar to sites of altered methylation previously described in the immunoglobulin heavy-chain enhancer. Treatment of isolated nuclei with DNase I or a variety of restriction endonucleases defined a B-cell-specific approximately 0.25-kilobase region of enhanced nuclease susceptibility similar to that observed in the murine kappa enhancer. The 130-base-pair DNA segment that shows high sequence conservation between human, mouse, and rabbit DNAs lies at the 5' end of the nuclease-susceptible region.