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Positioning and stability of nucleosomes on MMTV 3′LTR sequences

1998; Elsevier BV; Volume: 275; Issue: 3 Linguagem: Inglês

10.1006/jmbi.1997.1464

1089-8638

Andrew Flaus, Timothy J. Richmond,

DNA and Nucleic Acid Chemistry

Uniquely positioned nucleosomes were mapped in vitro on mouse mammary tumor 3′ long terminal repeat (MMTV 3′LTR) DNA at base-pair resolution. Nucleosome A assembly was strongly favored over nucleosome B, and heating of each as a mononucleosome caused migration to the ends of the DNA fragment at a unique rate. Taken together with DNA sequence analysis, this suggests why MMTV 3′LTV nucleosome positions reported upstream of vector-derived sequences conflict and also how flanking genomic sequences could modulate the promoter in in vivo situations. Importantly, nucleosomes are shown to migrate for significant distances along DNA under physiologically relevant conditions, and the actual rates have been measured directly in solution. Exact positioning and shifting over greater than 60 bp has important consequences for transcription factor access to this MMTV promoter and for the role of nucleosomes in general.