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PubMed1995

Impact of rearrangements on function and position of chromosomes in the interphase nucleus and on human genetic disorders.

A synthesis of numerous published data and my own observations reveal that chromatin structure in interphase is functional, dynamic and complex. I hypothesize that: (1) chromosome regions organize nuclear structures and thus their own environment (address themselves in sites and condensation patterns most appropriate for their functional state in the particular cell); (2) chromosome rearrangement could alter nuclear architecture and thus function; and (3) these ideas can explain the contribution of chromosome rearrangements, even in a balanced form, to human pathologic conditions.

Adult↗
PubMed1984

Localization of human U1 small nuclear RNA genes to band p36.3 of chromosome 1 by in situ hybridization.

U1 small nuclear RNA (U1 snRNA) is encoded by a large family of genes (30-125 copies/haploid genome) which are transcribed by RNA polymerase II. U1 snRNA is thought to function in gene splicing. Since the U1 genes were found to be greater than 20 kb apart by analyzing genomic phage clones, the chromosomal location of U1 genes in the human genome was determined using Southern filter analysis of DNA isolated from human-rodent somatic cell hybrids and by in situ hybridization. Human DNA digested with PvuII and probed with a U1-specific probe, pD2, show several major hybridizing fragments. Of these, two human PvuII fragments of 1.4 kb and 2.4 kb had unique mobilities compared to mouse fragments. In a study of 19 cell hybrids, the human-specific U1 fragments segregated with the chromosome 1 markers peptidase C and adenylate kinase 2. All other chromosomes showed greater than or equal to 19% discordancy . An additional 13 karyotyped cell hybrids, analyzed by Southern filter analysis, confirmed the assignment of this class of U1 genes to chromosome 1. Additional digests with MspI and PstI indicated that most U1 genes are located on chromosome 1. To determine if the U1 RNAs are located predominantly at one site or dispersed over chromosome 1, a tritium-labeled U1 probe was hybridized in situ to metaphase chromosomes. The majority of the grains were at band 1p36 .3, suggesting that most of the U1 genes are located in this region.

Animals↗
PubMed1995

A new mobile genetic element in Lactobacillus delbrueckii subsp. bulgaricus.

A new IS element (ISL3) was discovered in Lactobacillus delbrueckii subsp. bulgaricus during the characterization of the linkage relationships between the two genes important for milk fermentation, beta-galactosidase (lacZ) and the cell-wall associated protease (prtP). ISL3 is a 1494 bp element, flanked by 38 bp imperfect inverted repeats, and generates an 8 bp target duplication upon insertion. It contains one open reading frame, encoding a potential polypeptide of 434 amino acids, which shows significant homology (34% identity) to the transposase of the Leuconostoc mesenteroides element IS1165. Molecular analysis of spontaneous lacZ mutants revealed some strains that had sustained deletions of 7 to 30 kb in size, centered on and eliminating the copy of ISL3 next to lacZ. Other deletion endpoints were identified as located immediately adjacent to ISL3. Furthermore, genetic translocations that had occurred via transposition of ISL3 were observed fortuitously in cultures screened for deletion mutants. ISL3 can be found in one to several copies in various strains of L. delbrueckii. However, it was not present in other dairy lactic acid bacteria tested.

Amino Acid Sequence↗
PubMed2004

Asbestos induces tissue factor in Beas-2B human lung bronchial epithelial cells in vitro.

Asbestos has been implicated in the pathogenesis of interstitial lung diseases including asbestosis. Tissue factor (TF) initiates blood coagulation in vivo contributing to inflammation and tissue remodeling via extravascular fibrin deposition and signaling for profibrogenic mediators. We hypothesized that asbestos could induce TF expression by lung epithelial cells. We found that TF mRNA and TF-dependent procoagulant activity were induced in asbestos-treated Beas-2B human airway epithelial cells, which we used as a model system. The effect was increased by crocidolite and chrysotile versus control particulates, including titanium dioxide (TiO2) and Wollastonite (W). Transcription factors that bind the TF gene promoter, including NF-kappaB, AP1 and Sp1, were induced by asbestos while TF mRNA was unstable. TF mRNA was inhibited by mithramycin in asbestos-treated as well as control cells suggesting that Sp1 contributes to TF maintenance in Beas-2B cells. Sp1 knockdown with specific siRNA decreased TF antigen, which is consistent with Sp1-mediated control of TF in Beas-2B cells. The results demonstrate that asbestos induces TF expression in lung epithelial cells in vitro, representing a newly recognized potential mechanism by which asbestos may modulate epithelial cell responses germane to lung remodeling. The mechanism involves alterations in steady-state TF mRNA that do not involve posttranscriptional regulation, implicating control of TF gene expression at the transcriptional level through Sp1 or other transcription factors.

Asbestos↗
PubMed1998

Genetic mapping of the amide response element(s) of the hsr omega locus of Drosophila melanogaster.

Small chromosomal deletions [Df(3R)eR-1 and Df(3R)eP] with intact hsromega transcription units but with variable deletions of the upstream region were used to map the upstream regions that regulate heat shock and amide responsivity of the 93D puff (hsromega locus) in salivary glands of late third instar larvae of Drosophila melanogaster. The Df(3R)eP deletion, generated by a P-element mobilization screen, removed the 93B6-7 to 93D3-5 cytogenetic region. [3H]uridine-labeled transcription autoradiograms revealed that normal developmental and heat shock-induced expression of the 93D puff remained unaffected in both the deficiency chromosomes. However, the amide responsivity of the 93D site was lost on the Df(3R)eP homolog while the Df(3R)eR-1 homolog responded normally to amides. Southern hybridizations with a series of upstream probes mapped the distal breakpoint of the Df(3R)eP deletion between -22 kb and -23 kb of the hsromega transcription unit. Since the distal breakpoint of Df(3R)eR-1 is at about -45 kb upstream of the hsromega gene it is inferred that the amide response element(s) that modulate the specific transcriptional activation of the 93D puff following treatment of salivary glands with a variety of amides is/are located in the -22 kb to about -45 kb upstream interval. The Df(3R)eP and Df(3R)eR-1 deletions also abolished dosage compensation at the 93D locus as well as the effect of beta-alanine levels on its heat shock inducibility.

5' Untranslated Regions↗
PubMed1983

Eukaryotic genome: model considerations.

The paper presents a new model of chromosome structure based on the assumption that multiple circular subunits of DNA exist. The essential difference with previously described models is the circular DNA unit forms a central chromosome axis. Chromosome configurations during various phases of the cell cycle depend on the various conformations of this central integrating unit. The described model can be generalized for all haploid set of eukaryotic nucleus. Some aspects of the chromosome structure and their functions have been discussed.

Animals↗
PubMed1979

Deletion mutants of Xenopus laevis 5S ribosomal DNA.

Deletion mutants have been derived from a plasmid-cloned repeating unit of Xenopus laevis oocyte 5S DNA by introducing the transposable chloramphenicol-resistance element Tn9 into the AT-rich spacer sequence near the 5' terminus of the X. laevis 5S rRNA gene in a recombinant plasmid and then selecting plasmids which had lost the transposable element. Plasmids lacking the entire transposable element and various portions of the AT-rich spacer sequence flanking the original site of Tn9 integration have been obtained, and their ability to support transcription of the remaining X. laevis 5S rRNA gene has been tested in X. laevis oocyte nuclei. The deletion mutants analyzed in the present study retain the 49 nucleotide nonrepetitive sequence immediately adjacent to the 5' terminus of the gene, but lack as much as 80% of the repetitive AT-rich spacer sequence (Fedoroff and Brown, 1978). Such deletion mutants are fully active templates for 5S rRNA synthesis. This implies that the AT-rich spacer, which comprises half or more of each repeating unit in X. laevis oocyte 5S DNA, is relatively unimportant for correct initiation of transcription, and that if there are extragenic sequences with promoter function, they are likely to reside in the short nonrepetitive region immediately adjacent to the gene.

Animals↗
PubMed1984

Chromosome rearrangements in Trypanosoma brucei.

We have studied chromosome rearrangements in T. brucei using pulsed field gradient gel electrophoresis to separate chromosome-sized DNA molecules. We detect size changes in a set of small chromosomes (200-700 kb) at a frequency of 10(-5) to 10(-6) per trypanosome division; this results in a radical difference in the size distribution of these chromosomes in different T. brucei isolates. Several of these chromosome rearrangements can be related to a change in the expression of surface antigen genes. Such rearrangements may be undetectable by standard gel electrophoresis and Southern blot analysis because the DNA segment transferred is too large to detect the breakpoint with the antigen gene probe. We also provide additional evidence for the notion that transcription of protein-coding genes in T. brucei and related flagellates is discontinuous. The possibility that gene rearrangements are essential for all changes in variant surface gene expression remains open.

Animals↗