Metaphase chromosome structure: Bands arise from a differential folding path of the highly AT-rich scaffold

• Published in: Cell Vol. 76; no. 4; pp. 609 - 622
• Main Authors: Saitoh, Yasushi, Laemmli, Ulrich K.
• Format: Journal Article
• Language: English
• Published: Cambridge, MA Elsevier Inc 25.02.1994; Cell Press
• Subjects: Animals; Base Composition; Biological and medical sciences; Chromatin - ultrastructure; Chromatin. Chromosome; Chromosome Banding - methods; Chromosomes - ultrastructure; Daunorubicin; Deer; DNA Topoisomerases, Type II - metabolism; Fundamental and applied biological sciences. Psychology; High Mobility Group Proteins - metabolism; Metaphase; Molecular and cellular biology; Molecular genetics; Staining and Labeling; Vertebrata; Mammalia; Chromosome R banding; Fluorescent labelling; Metaphase; Chromosome Q banding; Chromosome; Skin; Artiodactyla; Ungulata; Structural analysis; Muntiacus muntjak
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/0092-8674(94)90502-9

Using the highly AT-specific fluorchrome daunomycin, a longitudinal optical signal called AT queue, thought to arise from a line-up of the highly AT-rich scaffold-associated regions (SARs) by the scaffolding, was identified in native chromosomes. Fluorescence banding is proposed to result from a differential folding path of the AT queue during its progression from telomere to telomere. The AT queue is tightly coiled or folded in a Q band, the resulting transverse striations across the chromatid, which also represent Giemsa subbands, generating a bright AT-rich signal over the Q region. The R bands, in contrast, contain a more central (unfolded) AT queue, yielding an AT-dull signal over the R regions. The AT queue is identified by immunofluorescence against topoisomerase II (topo II) and HMG-I Y as the scaffold of native chromosomes; the fluorescence signal from both proteins is akin to a detailed Q-type banding pattern. Native chromosomes appear assembled according to the loop-scaffold model.