title: Molecular and cytogenetic analysis of the heterochromatin-euchromatin junction region of the Drosophila melanogaster X chromosome using cloned DNA sequences.
abstract: We have used three cloned DNA sequences consisting of (1) part of the suppressor of forked transcription unit, (2) a cloned 359-bp satellite, and (3), a type I ribosomal insertion, to examine the structure of the base of the X chromosome of Drosophila melanogaster where different chromatin types are found in juxtaposition. A DNA probe from the suppressor of forked locus hybridizes exclusively to the very proximal polytenized part of division 20, which forms part of the beta-heterochromatin of the chromocenter. The cloned 359-bp satellite sequence, which derives from the proximal mitotic heterochromatin between the centromere and the ribosomal genes, hybridizes to the under replicated alpha-heterochromatin of the chromocenter. The type I insertion sequence, which has major locations in the ribosomal genes and in the distal mitotic heterochromatin of the X chromosome, hybridizes as expected to the nucleolus but does not hybridize to the beta-heterochromatic division 20 of the polytene X chromosome. Our molecular data reveal that the suppressor of forked locus, which on cytogenetic grounds is the most proximal ordinary gene on the X chromosome, is very close to the junction of the polytenized and non-polytenized region of the X chromosome. The data have implications for the structure of beta-heterochromatin-alpha-heterochromatin junction zones in both mitotic and polytene chromosomes, and are discussed with reference to models of chromosome structure.
authors.affiliation: Research School of Biological Sciences, Australian National University, Canberra City.
authors.forename: M T
authors.initials: MT
authors.lastname: Yamamoto
authors.forename: A
authors.initials: A
authors.lastname: Mitchelson
authors.forename: M
authors.initials: M
authors.lastname: Tudor
authors.forename: K
authors.initials: K
authors.lastname: O'Hare
authors.forename: J A
authors.initials: JA
authors.lastname: Davies
authors.forename: G L
authors.initials: GL
authors.lastname: Miklos
mesh_terms: D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D002843:Chromatin / Q000378:metabolism*; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D004331:Drosophila melanogaster / Q000235:genetics*; D022041:Euchromatin; D006570:Heterochromatin / Q000378:metabolism*; D007621:Karyotyping; D008938:Mitosis; D009693:Nucleic Acid Hybridization; D015183:Restriction Mapping; D012469:Salivary Glands / Q000378:metabolism; D013489:Suppression, Genetic; D014158:Transcription, Genetic; D014960:X Chromosome
chemical_list: D002843:Chromatin; D022041:Euchromatin; D006570:Heterochromatin; D004247:DNA