Nucleosome distribution on the Jk and Ck immunoglobulin gene segments of mouse liver chromatin.

The chromatin structure of the transcriptionally inactive kappa immunoglobulin gene in mouse liver was investigated by mainly employing indirect endlabeling on Bsp RI restriction nuclease digestions of intact nuclei. The disclosed strong (about 85%) but not uniform protection of the Bsp RI sites by nucleosomes is inconsistent with both a uniquely sequence-oriented localization and a completely random distribution of nucleosomes in this region of the genome. Several possibly applicable models are discussed.

Protection of expressed immunoglobulin genes against nuclease cleavage.

Fragmentation of the actively transcribed kappa immunoglobulin gene in mouse myeloma nuclei with micrococcal nuclease and the restriction nuclease Bsp RI reveals a chromatin structure without the regularity of repeating nucleosomes found in bulk chromatin. Such regularity is restored about 2.2 kb 3' of the coding region.

Differences in the nuclease sensitivity between the two alleles of the immunoglobulin kappa light chain genes in mouse liver and myeloma nuclei.

In mouse myeloma T the productive kappa light chain gene differs from its aberrantly rearranged allele in the patterns of DNAase I hypersensitive sites. In the region of the alleles where they are identical in sequence they have one site in common which lies 0.8 kb downstream of the coding region; but two sites upstream of and within the C gene segment (2) are found only on the non-productive allele.

DNA-histone interactions in nucleosomes.

We have utilized micrococcal nuclease digestion and thermal denaturation studies to investigate the binding of DNA to the histone core of the nucleosome. We conclude that a total of approximately 168 base pairs (bp) of DNA can interact with the histone core under appropriate solution conditions, even in the absence of lysine-rich histones. The interactions in this total length of DNA can be divided into three classes: (a) approximately 22 bp at the ends is bound only at moderate ionic strength.

Nuclease digestion promotes structural rearrangements in H1-depleted chromatin.

Digestion of H1-depleted chromatin with micrococcal nuclease at an ionic strength of 0.35M gives rise to structural rearrangements indicating nucleosomal sliding. The ionic strength necessary to reveal this effect is significantly lower than that required in the absence of an accompanying digestion.