title: The 30 nm chromatin fiber as a flexible polymer.
abstract: Our analysis of the data of van den Engh, Sachs, and Trask (Science 257, 1410 (1992)), for the dependence of the mean square distance between pairs of hybridization sites (< L2n >, micron 2) on the known genomic distance (n, bp) separating these sites on chromosome number 4 in G1 human fibroblast nuclei, shows that < L2n > is proportional to n2v with v = 3/5 for n < 1 Mbp. The v-value of 3/5 is characteristic of flexible polymer chains with excluded volume effects in dilute good solutions. Since the DNA concentration in nuclei is very high (ca. 1-10 mg/ml), and theory (Flory, J. Chem. Phys. 17, 303, 1949) predicts v = 1/2 for overlapping polymers, the finding of v = 3/5 means that the chromatin fibers do not overlap in interphase nuclei. The dependence of < L2n > on n for n < 4 Mbp is consistent with the model of large (approximately 6 Mbp, 3 microns diameter) loops of interphase chromatin attached to nuclear membrane sites. Using the constant (e.g., Widom, Ann. Rev. Biophys. Biophys. Chem. 18, 365 (1989)) and variable (Williams & Langmore, Biophys. J. 59, 606 (1991)) diameter fiber models, the Kuhn statistical segment of the 30 nm chromatin fiber was estimated to have a length of 196-272 nm with a corresponding DNA content of 21-37 kbp.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: State University of New York, Health Science Center at Brooklyn 11203.
authors.forename: J Y
authors.initials: JY
authors.lastname: Ostashevsky
authors.forename: C S
authors.initials: CS
authors.lastname: Lange
mesh_terms: D001704:Biopolymers; D002467:Cell Nucleus / Q000737:chemistry; D002843:Chromatin / Q000737:chemistry* / Q000648:ultrastructure; D004247:DNA / Q000032:analysis / Q000737:chemistry*; D005347:Fibroblasts; D006801:Humans; D007399:Interphase; D008433:Mathematics; D011487:Protein Conformation; D012016:Reference Values
chemical_list: D001704:Biopolymers; D002843:Chromatin; D004247:DNA