title: The Ag-NOR proteins present a crescent-shaped distribution at the secondary constrictions of metaphase PtK1 chromosomes.
abstract: The ultrastructural distribution of the proteins responsible for the silver staining of NORs was analyzed on serial thin sections of preembedded silver-stained rat kangaroo PtK1 metaphase chromosomes. Our results show that the Ag-NOR proteins present a crescent-shaped distribution at the secondary constriction of each chromatid. Moreover, in some cases the crescent-shaped structures of both chromatids are not symmetrically arranged but show different orientations. These observations, together with our own and previously reported light microscopy results obtained on silver-stained mammalian chromosomes, lead us to suggest a mechanism for the formation of apparent secondary constrictions at NORs.
authors.affiliation: Departamento de Biología, Universidad Autónoma de Madrid, Spain. jasuja@ccuam3.sdi.uam.cs
authors.forename: J A
authors.initials: JA
authors.lastname: Suja
authors.forename: D
authors.initials: D
authors.lastname: Hernandez-Verdun
mesh_terms: D000818:Animals; D001399:Azure Stains; D002460:Cell Line; D002842:Chromatids / Q000737:chemistry / Q000648:ultrastructure; D002871:Chromosome Banding; D002875:Chromosomes / Q000737:chemistry* / Q000648:ultrastructure; D007614:Macropodidae; D008677:Metaphase; D008854:Microscopy, Electron; D009687:Nuclear Proteins / Q000032:analysis*; D009697:Nucleolus Organizer Region / Q000737:chemistry* / Q000648:ultrastructure; D016622:Silver Staining; D014960:X Chromosome / Q000737:chemistry / Q000648:ultrastructure
chemical_list: D001399:Azure Stains; D009687:Nuclear Proteins