ABSTRACT
The transposable element TE35B carries two copies of the white (w) gene at 35B1.2 on the second chromosome. These w genes are suppressed in zeste-1 (z1) mutant background in a synapsis-dependent manner. Single-copy derivatives of the original TE35B stock give red eyes when heterozygous, but zeste eyes when homozygous. TE35B derivatives carrying single, double or triple copies of w were crossed to generate flies carrying from two to five ectopic w genes. Within this range, z1-mediated suppression is insensitive to copynumber and does not distinguish between w genes that are in cis or in trans. Suppression does not require the juxtaposition of even numbers of w genes, but is extremely sensitive to chromosomal topology. When arranged in a tight cluster, in triple-copy TE derivatives, w genes are nonsuppressible. Breakpoints falling within TE35B and separating two functional w genes act as partial suppressors of z1. Similarly, breakpoints immediately proximal or distal to both w genes give partial suppression. This transvection-dependent downregulation of w genes may result from mis-activation of the X-chromosome dosage compensation mechanism.
Subject(s)
ATP-Binding Cassette Transporters , DNA Transposable Elements , Drosophila Proteins , Drosophila melanogaster/genetics , Eye Proteins , Genes, Insect , Insect Proteins/genetics , Transfection , Animals , Chromosome Aberrations , Chromosome Mapping , Crosses, Genetic , Female , Male , Mutation , Nucleic Acid Conformation , Phenotype , Pigments, BiologicalABSTRACT
A physical map of the euchromatic X chromosome of Drosophila melanogaster has been constructed by assembling contiguous arrays of cosmids that were selected by screening a library with DNA isolated from microamplified chromosomal divisions. This map, consisting of 893 cosmids, covers approximately 64% of the euchromatic part of the chromosome. In addition, 568 sequence tagged sites (STS), in aggregate representing 120 kb of sequenced DNA, were derived from selected cosmids. Most of these STSs, spaced at an average distance of approximately 35 kb along the euchromatic region of the chromosome, represent DNA tags that can be used as entry points to the fruitfly genome. Furthermore, 42 genes have been placed on the physical map, either through the hybridization of specific probes to the cosmids or through the fact that they were represented among the STSs. These provide a link between the physical and the genetic maps of D. melanogaster. Nine novel genes have been tentatively identified in Drosophila on the basis of matches between STS sequences and sequences from other species.
Subject(s)
Chromosome Mapping , Cosmids , Drosophila melanogaster/genetics , Sequence Tagged Sites , X Chromosome , Amino Acid Sequence , Animals , Base Sequence , DNA , Molecular Sequence Data , Sequence Homology, Amino AcidABSTRACT
The el-noc complex spans a distance of about 200 kb on chromosome 2L. It consists of three discrete genetic regions el, l(2)35Ba and noc, each of which has a distinct phenotype when mutant. The noc locus itself is complex, including three separate regions. The el locus has been characterized by mapping 30 aberration breakpoints to the DNA. It extends over a distance of about 80 kb. It can be divided into two parts by the aberrations In(2LR)DTD128 and T(Y;2)A80. These break between two sets of el alleles yet are both phenotypically wild type for elbow. The simplest explanation is that el consists of two transcription units elA and elB. The locus pu, which appears to be unrelated to the el-noc complex, is found to map between the two el loci very close to elB (the distal el locus). The loci l(2)35Ba and nocA have been separated by only two l(2)35Ba+nocA- deletions and a nocA- inversion. No l(2)35Ba-nocA+ aberrations have been found. At the molecular level these loci are found to occupy almost the same region, and are probably identical.
