Metaphase chromosome structure: bands arise from a differential folding path of the highly AT-rich scaffold.
Using the highly AT-specific fluorochrome 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.
Saitoh
Y
Y
Department of Biochemistry, University of Geneva, Switzerland.
Laemmli
U K
UK
D000818:Animals; D001482:Base Composition; D002843:Chromatin / Q000648:ultrastructure; D002871:Chromosome Banding / Q000379:methods*; D002875:Chromosomes / Q000648:ultrastructure*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D003630:Daunorubicin; D003670:Deer; D006609:High Mobility Group Proteins / Q000378:metabolism; D008677:Metaphase; D013194:Staining and Labeling
D002843:Chromatin; D006609:High Mobility Group Proteins; D004250:DNA Topoisomerases, Type II; D003630:Daunorubicin