Transcribed Chromatin Exhibits an Altered Nucleosomal Spacing

The nucleosomal repeat lengths of bulk chromatin and the chromatin of transcriptionally active and inactive genes were analyzed in two mouse cell lines and adult mouse spleens. The adult β -globin gene exhibits a nucleosomal repeat length approximately 11 base pairs longer than (i) an inactive embryonic globin gene, ε y3; (ii) an immunoglobulin heavy chain gene, Cμ; and (iii) the bulk chromatin in murine erythroleukemia cell line DS19. The repeat length of the Cμgene was approximately 14 base pairs longer than that of the adult β -globin or ε y3 genes in the IgM-producing cell line M104E. The chromatin of several inactive genes had repeat lengths less than or equal to bulk chromatin. Individual genes were shown to vary in repeat length among the cell types examined. In addition, genes that exhibited an increased nucleosomal spacing were digested to mononucleosomes more rapidly than bulk chromatin or inactive genes with shorter repeats. Increased repeat length was also correlated with an increased sensitivity to DNase I. Thus, increased nucleosomal spacing may be a property of transcriptionally active genes or genes with the potential for transcription.