Biomedical subjects

A Shihab-el-Deen

Publications and source records attributed to A Shihab-el-Deen.

5 recordsLinked to original sources

PubMed1994

Electron microscopic analysis of in vitro replication products of ors 8, a mammalian origin enriched sequence.

Electron microscopy was used to map the initiation site of ors 8 DNA replication in vitro in a system that is capable of initiating and supporting one round of semiconservative replication of cloned mammalian DNA origin-enriched sequences (ors). Using unique restriction sites in ors 8 plasmid DNA, we have mapped the replication bubble within the monkey DNA sequence. In addition to site-specific initiation within the ors, the results also indicate bidirectional replication.

Animals↗

PubMed1993

Chromosomal localization of a sequence with in vivo activity for initiation of DNA replication.

The genomic fragment containing the sequence of human cDNA clone 343, previously characterized as capable of autonomous replication upon transfection into mammalians cells and occupying a genomic region inclusive of an initiation zone for DNA replication, was mapped on human chromosome 6q22-qter by a combination of in situ hybridization and G-banding. Southern blot hybridization with a panel of human-hamster somatic cells confirmed the location of the 343 gene on chromosome 6. Fragile sites have been mapped to the region at 6q21 and 6q26. Several neoplastic disorders, including melanoma, acute nonlymphocytic leukemia, acute lymphocytic leukemia, and malignant lymphoma, have also exhibited translocations and deletions involving the region 6q21-6q27.

Animals↗

PubMed1992

ORS12, a mammalian autonomously replicating DNA sequence, is present at the centromere of CV-1 cell chromosomes.

ors12, an 812-bp-long sequence, previously isolated by extrusion of nascent DNA from replication bubbles active at the onset of S phase (G. Kaufmann, M. Zannis-Hadzopoulus, and R. G. Martin Mol. Cell. Biol. 5, 721-727, 1985), has been shown to function as an origin of DNA replication in autonomously replicating plasmids (L. Frappier and M. Zannis-Hadjopoulos Proc. Natl. Acad. Sci. USA 84, 6668-6672, 1987) and in a cell-free system (C. E. Pearson, L. Frappier, and M. Zannis-Hadzopoulos Biochim. Biophys. Acta 1090, 156-166, 1991). A portion of ors12 (nucleotides 1-168) consists of the highly reiterated alpha-satellite sequence (B. S. Rao et al. Gene 87, 233-242, 1990). We have estimated the copy number of the non-alpha-satellite portion of ors12 in CV-1 cells to be < 9 copies per haploid genome and have used it as a probe to generate a genomic map of ors12 on CV-1 DNA. In situ hybridization of CV-1 metaphase chromosomes, using a biotinylated probe of the entire ors12 sequence, positively identified the centromeres of all chromosomes. However, when the non-alpha-satellite portion of ors12 was used as a probe, it positively identified the centromeric region of only six chromosomes, namely, B4, C11, D14, D24, E25, and E27, as well as that of a marker chromosome. The results suggest that ors12 represents a centromeric putative replication origin that is present on a subset of CV-1 chromosomes and is activated at the onset of S phase.

Animals↗

PubMed1991

DNA cruciforms and the nuclear supporting structure.

Cruciforms have been suggested as potential recognition structures at or near origins of DNA replication in eukaryotic cells. Monoclonal antibodies with structural specificity for DNA cruciforms have been produced (Frappier et al. J. Mol. Biol. 193, 751, 1987). The effect of these antibodies, when introduced into permeabilized cells, was to increase overall DNA synthesis and relative copy number of genes (Zannis-Hadjopoulos et al. EMBO J. 7, 1837, 1988); this was interpreted to be a consequence of antibody stabilization of the cruciforms located at or near replication origins resulting in multiple initiations of DNA replication at a single site. Fluorescent labeling of nuclei with anti-cruciform antibodies produces a nonuniform pattern of fluorescence in cells arrested at the G1/S boundary which then changes with progression through S-phase (Ward et al. Exp. Cell Res. 188, 235, 1990). In order to determine the relationship of cruciform distribution in DNA with the nuclear matrix/chromosomal scaffold, we assessed the susceptibility of DNA containing cruciforms to digestion with DNase I. The majority of the cruciforms detectable at G1/S and throughout the nucleus are readily digested by DNase, suggesting that cruciform structures may not be intimately associated with matrix proteins. The fraction that is resistant to DNase I appears associated with nuclear membrane and the nucleolus. No cruciforms could be detected in metaphase chromosomes; cruciforms either are not present or are inaccessible--buried in the scaffold. The absence of cruciforms from metaphase chromosomes would be consistent with the viewpoint that the cruciform in vivo is a transient structure dependent upon and interacting with proteins essential for replication or transcription.

Animals↗

PubMed1987

Bone marrow cultures in dysmyelopoietic syndrome: diagnostic and prognostic evaluation.

Thirty-four patients with a probable clinical diagnosis of dysmyelopoietic syndrome (DMPS) were studied to assess the in vitro growth pattern of their hemopoietic progenitors, i.e. burst-forming unit erythroid (BFU-E) and colony-forming unit myeloid (CFU-C) progenitor cells. Twenty-one patients had DMPS confirmed by final diagnosis and were classified according to the French-American-British (FAB) recommendations. Our results indicate that the normal colony growth of hemopoietic progenitors in vitro excludes DMPS and other preleukemic conditions. In addition, within the DMPS group a low number of CFU-C (11 colonies or fewer) was a highly significant indicator for the development of acute leukemia. Analysis of the limited number of cytogenetic results in the DMPS patients did not reach statistical significance in relation to the development of acute leukemia.

Bone Marrow↗