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PubMed1988

Efficiency of homologous DNA recombination varies along the Bacillus subtilis chromosome.

Structures consisting of a genetic marker (erythromycin or kanamycin resistance, thymidylate synthetase) flanked by 3.4-kilobase direct repeats (pBR322 sequences) were inserted in 12 different locations of the Bacillus subtilis chromosome. Recombination between the repeats was followed by the loss of the genetic marker. Recombination frequencies found in different locations varied from 1.2 X 10(-5) to 40 X 10(-5) per cell generation. Such differences were highly significant (P less than 0.001).

Bacillus subtilis↗
PubMed1988

Chromosome instability associated with human alphoid DNA transfected into the Chinese hamster genome.

Repetitive DNA sequences have been implicated in the mediation of DNA rearrangement in mammalian cells. We have tested this hypothesis by using a dihydrofolate reductase (DHFR) expression vector into which candidate sequences were inserted. DHFR- Chinese hamster ovary (CHO) cells were transfected with this vector, the amplification of which was then selected for by methotrexate (MTX) exposure. Cells transfected with the vector alone (and resistant to 0.02 or 1.0 microM MTX) or with a poly(dG-dT) insert (and resistant to 0.05 or 1.0 microM MTX) showed little change in chromosome aberrations or sister chromatid exchange frequencies. In contrast, transfection of DHFR- CHO cells with a vector containing either of two distinct 0.34-kilobase human alphoid DNA segments (and selection to 0.05 to 10.0 microM MTX) showed an approximately 50% increase in chromosome number and marked changes in chromosome structure, including one or two dicentric or ring forms per cell. The sister chromatid exchange frequency also increased, to more than double the frequency of that in cells transfected without insert or those containing poly(dG-dT). In situ hybridization of one 0.34-kilobase insert in some cells suggested clustering of homologous sequences in structurally abnormal recipient CHO cell chromosomes. The approach described provides an introduction to a unique means for a coordinate molecular and cytological study of dynamic changes in chromosome structure.

Animals↗
PubMed1995

Human estrogen sulfotransferase gene (STE): cloning, structure, and chromosomal localization.

Sulfation is an important pathway in the metabolism of estrogens. We recently cloned a human liver estrogen sulfotransferase (EST) cDNA. We have now determined the structure and chromosomal localization of the EST gene, STE, as a step toward molecular genetic studies of the regulation of EST in humans. STE spans approximately 20 kb and consists of 8 exons, ranging in length from 95 to 181 bp. The locations of most exon-intron splice junctions within STE are identical to those found in a human phenol ST (PST) gene, STM, and in a rat PST gene. In addition, the locations of five STE introns are also conserved in the human dehydroepiandrosterone (DHEA) ST gene, STD. The 5'-flanking region of STE contains one CCAAT and two TATA sequences. The location of one of the TATA box elements is in excellent agreement with the site of transcription initiation as determined by 5'-rapid amplification of cDNA ends. STE was mapped to human chromosome 4q13.1 by fluorescence in situ hybridization. Cloning and structural characterization of STE will now make it possible to study potential molecular genetic mechanisms involved in the regulation of EST in human tissues.

Amino Acid Sequence↗
PubMed1991

Structure and chromosomal location of the gene for endothelial-leukocyte adhesion molecule 1.

Endothelial-leukocyte adhesion molecule 1 is a cell surface glycoprotein expressed by cytokine-activated endothelium that mediates the adhesion of blood neutrophils. Endothelial-leukocyte adhesion molecule 1 is a member of the selectin family of cell adhesion molecules each of which contain an amino-terminal lectin-like domain, followed by an epidermal growth factor-like domain and a variable number of short consensus repeats similar to those found in complement binding proteins. Genomic clones encoding the ELAM gene were isolated and the organization of the ELAM gene was determined. The gene, which is present in a single copy in the human genome, contains 14 exons spanning about 13 kilobases of DNA. The positions of exon-intron boundaries correlate with the putative functional subdivisions of the protein. Introns are found at similar positions in all of the six complement regulatory repeats, suggesting that these elements arose by internal gene duplication. A consensus TATAA element is located upstream of the transcriptional start site. The ELAM promoter contains an inverted CCAAT box and consensus NF-kappa B- and AP-1-binding sites. The ELAM gene was assigned to the q12 greater than qter region of human chromosome 1 by analysis of human-mouse hybrid cell lines. Two other members of the selectin gene family, the leukocyte adhesion molecule 1 (LAM-1, TQ1, LEC-CAM 1, or Leu-8) and the granule membrane protein 140 (GMP-140, PADGEM, or CD62) have been localized to the long arm of chromosome 1, as have the structurally related complement binding proteins, suggesting that these genes may share a common evolutionary history.

Amino Acid Sequence↗
PubMed2004

Telomere shortening occurs early during breast tumorigenesis: a cause of chromosome destabilization underlying malignant transformation?

Chromosomal instability appears early during breast carcinogenesis and is considered a major driving force in malignant transformation. While current evidence suggests that centrosomal and mitotic checkpoint defects may, in large part, account for numerical chromosomal abnormalities, the mechanisms underlying structural chromosomal abnormalities remain largely unknown. Telomeres stabilize and protect chromosomal termini, but shorten due to cell division and oxidative damage. Moderate telomere shortening signals a tumor suppressive growth arrest in normal cells. Critically short telomeres, in the setting of abrogated DNA damage checkpoints, cause chromosomal instability due to end-to-end chromosomal fusions, subsequent breakage, and rearrangement, resulting in an increased cancer incidence in animal models. Recent results from high resolution in situ telomere length assessment in human breast tissues indicate that significant telomere shortening is prevalent in preinvasive breast lesions (DCIS), as well as focal areas of histologically normal epithelium from which breast carcinoma is thought to arise. Telomere shortening is therefore a strong candidate for the cause of structural chromosome defects that contribute to breast cancer development.

Breast Neoplasms↗
PubMed1992

Mutants of the microtubule motor protein, nonclaret disjunctional, affect spindle structure and chromosome movement in meiosis and mitosis.

The Drosophila microtubule motor protein, nonclaret disjunctional (ncd), is required for proper chromosome distribution in meiosis and mitosis. We have examined the meiotic and mitotic divisions in wild-type Drosophila oocytes and early embryos, and the effects of three ncd mutants (cand, ncd and ncdD) on spindle structure and chromosome movement. The ncd mutants cause abnormalities in spindle structure early in meiosis I, and abnormal chromosome configurations throughout meiosis I and II. Defective divisions continue in early embryos of the motor null mutant, cand, with abnormal early mitotic spindles. The effects of mutants on spindle structure suggest that ncd is required for proper meiotic spindle assembly, and may play a role in forming or maintaining spindle poles in meiosis. The disruption of normal meiotic and mitotic chromosome distribution by ncd mutants can be attributed to its role as a spindle motor, although a role for ncd as a chromosome-associated motor protein is not excluded. The ncd motor protein functions not only in meiosis, but also performs an active role in the early mitotic divisions of the embryo.

Animals↗
PubMed2000

Dynamics of beta and proliferating cell nuclear antigen sliding clamps in traversing DNA secondary structure.

Chromosomal replicases of cellular organisms utilize a ring shaped protein that encircles DNA as a mobile tether for high processivity in DNA synthesis. These "sliding clamps" have sufficiently large linear diameters to encircle duplex DNA and are perhaps even large enough to slide over certain DNA secondary structural elements. This report examines the Escherichia coli beta and human proliferating cell nuclear antigen clamps for their ability to slide over various DNA secondary structures. The results show that these clamps are capable of traversing a 13-nucleotide ssDNA loop, a 4-base pair stem-loop, a 4-nucleotide 5' tail, and a 15-mer bubble within the duplex. However, upon increasing the size of these structures (20-nucleotide loop, 12-base pair stem-loop, 28-nucleotide 5' tail, and 20-nucleotide bubble) the sliding motion of the beta and proliferating cell nuclear antigen over these elements is halted. Studies of the E. coli replicase, DNA polymerase III holoenzyme, in chain elongation with the beta clamp demonstrate that upon encounter with an oligonucleotide annealed in its path, it traverses the duplex and resumes synthesis on the 3' terminus of the oligonucleotide. This sliding and resumption of synthesis occurs even when the oligonucleotide contains a secondary structure element, provided the beta clamp can traverse the structure. However, upon encounter with a downstream oligonucleotide containing a large internal secondary structure, the holoenzyme clears the obstacle by strand displacing the oligonucleotide from the template. Implications of these protein dynamics to DNA transactions are discussed.

Base Pairing↗
PubMed1988

Human sperm chromosome complements after microinjection of hamster eggs.

A technique was developed for microinjection of human spermatozoa into golden hamster (Mesocricetus auratus) eggs to obtain human pronuclear chromosome complements. Before microinjection the spermatozoa were treated by brief sonication or incubation in TEST-yolk buffer to reduce motility. Very few sperm chromosome complements developed after sperm treatment with sonication and the frequency of spermatozoa with structural chromosomal abnormalities was exceedingly high (91%). The majority of sperm chromosome complements analysed had multiple breaks and rearrangements. Sperm incubation in TEST-yolk buffer before microinjection provided more analysable sperm karyotypes with a significantly lower frequency of structural chromosomal abnormalities (39%, P less than 0.001). Our results therefore suggest that sonication induces structural chromosomal abnormalities in spermatozoa. Since the frequency of chromosomal abnormalities after microinjection was higher than after sperm fertilization of hamster eggs, it appears that microinjection per se may also increase the frequency of chromosomal abnormalities in spermatozoa. These results are based on small numbers and must be confirmed on larger sample sizes, but our study suggests that microinjection of spermatozoa into eggs should not be recommended for clinical use until fully evaluated.

Animals↗
PubMed2002

Changes in chromosomal surface structure by different isolation conditions.

The human cell cycle was synchronized and the chromosomes were isolated by a centrifugation method using two representative solutions for chromosome isolation (a polyamine buffer, PAB and citric acid solution, CAS) and fixatives. The centrifugation method yielded sufficient amounts of human metaphase chromosomes. Observation of the isolated chromosomes by scanning electron microscopy (SEM) revealed two types of surface structure which have been repeatedly reported to date: the human chromosomes in the PAB were relatively smooth but covered irregularly with scaly structures, while the surface of the chromosomes in the CAS exhibited a dense fibrous structure with a uniform diameter of 50-70 nm. Comparison of proteins extracted from chromosomes isolated with the PAB and CAS clearly indicated the removal of linker histones, H1, from chromosomes isolated with the CAS. These findings imply that the two different images of human chromosomes frequently observed by SEM are due to the removal of peripheral chromosomal materials including linker histones and/or the depletion of linker histones which prevent the surface chromatin fibers from scattering.

Cell Cycle↗
PubMed1989

Chromosome-breaking structure in maize involving a fractured Ac element.

Chromosome breakage in maize can result from an interaction between certain transposable elements. When an Ac (Activator) element and a state I Ds (Dissociation) element are present together in the genome, either linked or unlinked, breaks occur regularly at the locus of the Ds element. We show here that breaks occur with high frequency at or near the locus of a structure consisting of a 2.5-kilobase (kb) terminally deleted or fractured Ac element very tightly linked to a second, intact 4.6-kb Ac element. This structure has the features of a macrotransposon and may behave like one. Loss of the tight linkage abolishes chromosome breakage. A model based on transposition of the macrotransposon is proposed to explain the chromosome-breaking properties of Ac and Ds.

Alleles↗
PubMed1993

The need to reevaluate trisomy screening for advanced maternal age in prenatal diagnosis.

OBJECTIVES: Fluorescence in situ hybridization aneuploidy screening promises immediate results. To evaluate aneuploidy screening in prenatal diagnosis, the prenatal records at Oregon were reviewed. STUDY DESIGN: Karyotype reports of 7240 amniocentesis samples referred for advanced maternal age were retrospectively reviewed for numeric and structural chromosome abnormalities. RESULTS: The frequency of abnormal karyotypes was 2.5%; 1.4% were age-related trisomies and sex-chromosome aneuploids, and 1.1% were non-age-related abnormalities. The incidence of structural rearrangements was 0.9%, of which 70% were familial but not suspected on the basis of family history. CONCLUSIONS: Structural chromosome abnormalities were twice as common as previously reported, representing a significant unrecognized risk for subsequent pregnancies and other family members. Fluorescence in situ hybridization aneuploidy screening would not routinely detect structural chromosome abnormalities, which were twice as frequent as numeric aneuploidy at age 35 years. Routine use of fluorescence in situ hybridization for prenatal diagnosis should not be adopted without a prospective study of its accuracy, reliability, and impact on prenatal diagnosis.

Amniocentesis↗
PubMed1998

Chromosome number and structure both are markedly stable in RER colorectal cancers and are not destabilized by mutation of p53.

Fourteen colorectal cancer cell lines, categorized according to the presence or absence of microsatellite instability, were further analysed for chromosomal stability by karyotyping. NonRER (microsatellite stable) cell lines typically displayed highly aberrant karyotypes with alterations not only of chromosome number but also of chromosome structure including chromosomal deletions, inversions, and translocations. RER (microsatellite unstable) cell lines, in contrast, displayed significantly fewer alterations of chromosome number. Moreover, RER cell lines also displayed significantly fewer cytogenetically evident alterations of chromosome structure. Compared to NonRER colon cancers, RER colon cancers are significantly less likely to have undergone chromosomal gain, loss, or breakage. Characterization of p53 gene status by gene sequencing was performed in an attempt to determine if p53 gene status correlated with the chromosomal stability of the RER cancers. Gene mutations in p53 were present in all of the NonRER colon cancers. However, p53 gene mutations were also found present in four of nine of the RER colon cancers. Unexpectedly, RER colon cancers bearing mutant p53 demonstrated the same stability of chromosome number, and the same stability of chromosome structure, as the RER colon cancers with wild-type p53. Therefore, in RER colon cancers specific p53 independent mechanisms actively maintain the stability of both chromosome number and structure.

Chromosome Aberrations↗
PubMed2005

Characterization of a familial balanced rec(13) in a child with mild MR and his half-sibling with two structurally rearranged chromosomes 13.

In this report, we describe a 7-year-old child with mild mental retardation, developmental delay, and learning disabilities. His karyotype contained a rearrangement of chromosome 13, which appeared to include a duplication of 13q31-qter and a deletion of 13p12-pter regions. The chromosomal origin of the additional material was confirmed by fluorescence in situ hybridization (FISH) using a whole chromosome painting probe specific for chromosome 13. Family studies showed that his mother carried a balanced inversion of chromosome 13 and that his half-brother carried the balanced pericentric inversion of chromosome 13 from his mother as well as another structural rearrangement involving chromosome 13 presumably from his father. The findings from this study suggested that the proband's abnormal 13 resulted from an unbalanced crossing-over between the normal and maternal inverted chromosome 13.

Abnormalities, Multiple↗
PubMed2005

Post-irradiation phosphorylation of structural maintenance chromosome 1 (SMC1) is independent of the Fanconi protein pathway.

PURPOSE: To confirm the sensitivity of cells from patients with Fanconi anemia (FA) to ionizing radiation, and to determine whether the phosphorylation of structural maintenance chromosome 1 (SMC1) was associated with radiosensitivity, as it is in other DNA repair disorders. METHODS AND MATERIALS: Using lymphoblastoid cell lines from FA patients before and after exposure to ionizing radiation, the colony survival assay, radioresistant DNA synthesis, and SMC1 phosphorylation were measured. FA lymphoblastoid cell lines that had been transfected with the wild-type FANC gene were used as controls. RESULTS: Cells from FA patients of six complementation groups were radiosensitive. Despite this, SMC1 phosphorylation was normal in each case; radioresistant DNA synthesis, a measure of S phase checkpoint integrity, was defective in FANCD2 lymphoblastoid cell lines and was corrected in FANCD2 + D2 cells. CONCLUSIONS: The data indicate that the FANC pathway proteins play a major role in the cellular responses to ionizing radiation, but not in SMC1 phosphorylation or in the S phase checkpoint of FANCD2-deficient cells. Thus, SMC1 activation is not a common denominator of radiosensitivity, as has been suggested by radiation responses of cells from ataxia-telangiectasia, Nijmegen breakage syndrome, or Mre11 deficiency patients.

Cell Cycle Proteins↗
PubMed2001

Chromosome aberrations study of pupils in high radon level elementary school.

The ICRP Publication 65 recommends 200-600 Bq x m(-3) as the indoor radon action level for the general public. In Slovenia, a value of 400 Bq x m(-3) has been proposed but not yet approved. In a nation-wide radon project financed by the Health Inspectorate of Slovenia, it was discovered that the elementary school named "S3" belongs to a group of schools with elevated winter indoor radon concentrations up to 7,000 Bq x m(-3). Opening windows and doors during classes substantially decreased radon concentrations, but very seldom below 1,000 Bq x m(-3). Yearly effective doses for pupils, estimated according to ICRP 65, ranged from 7 to 11 mSv. Because the pupils have been subjected to the elevated radon concentrations, special preventive health checks have been performed. The examination protocol included mutagenetic tests, one for structural chromosomal aberrations and the other a micronucleus test. Altogether 85 pupils (37 girls and 48 boys) from the first four grades between the ages of 9 and 12 y were examined. An increase in cytogenetic damage was found for these pupils, compared to the control group, composed of pupils of the same age from another area with indoor radon concentrations in their school of below 400 Bq x m(-3). The incidence of structural chromosomal aberrations reached 2.0% (0.5-4) and micronucleus test was 6.52 per 500 cells with a maximum of 15 in some cases. In the control group structural chromosomal aberrations varied from 0.5 to 2.5%, while the maximum incidence of micronucleus was 9 micronucleus per 500 CB cells. The results obtained are preliminary and suggest a need to expand the study. A long-term radon survey, at least over a year, of the homes and wider residential environment of the pupils would be necessary to assess the correlation between radon exposure and both structural chromosomal aberrations and micronucleus findings.

Air Pollution, Indoor↗
PubMed1982

Yeast centromere DNA is in a unique and highly ordered structure in chromosomes and small circular minichromosomes.

We have examined the chromatin structure of the centromere regions of chromosomes III and XI in yeast by using cloned functional centromere DNAs (CEN3 and CEN11) as labeled probes. When chromatin from isolated nuclei is digested with micrococcal nuclease and the resulting DNA fragments separated electrophoretically and blotted to nitrocellulose filters, the centromeric nucleosomal subunits are resolved into significantly more distinct ladders than are those from the bulk of the chromatin. A discrete protected region of 220-250 bp of CEN sequence flanked by highly nuclease-sensitive sites was revealed by mapping the exact nuclease cleavage sites within the centromeric chromatin. On both sides of this protected region, highly phased and specific nuclease cutting sites exist at nucleosomal intervals (160 bp) for a total length of 12-15 nucleosomal subunits. The central protected region in the chromatin of both centromeres spans the 130 bp segment that exhibits the highest degree of sequence homology (71%) between functional CEN3 and CEN11 DNAs. This unique chromatin structure is maintained on CEN sequences introduced into yeast on autonomously replicating plasmids, but is not propagated through foreign DNA sequences flanking the inserted yeast DNA.

Base Sequence↗
PubMed2005

The topology of early- and late-replicating chromatin in differentially decondensed chromosomes.

In this study we used a novel technique to reveal both longitudinal and transverse differentiation within mammalian mitotic chromosomes. Structural changes in chromosomes that we term 'differential decondensation' were produced in cells that were first incubated in hypotonic medium (15% Hanks' solution), then adapted to normotonic conditions and thereafter exposed to a second short hypotonic shock. Such a double hypotonic treatment (DHT) is not critical for cell viability, but considerably elongates the G2 phase of the cell cycle. Giemsa staining of differentially decondensed chromosomes corresponds to standard G-banding, but does not need the standard post-fixation treatment. Using 'dynamic' BrdU banding, we show that such 'differential' staining is a result of differential resistance of the R- and G-bands to DHT. Thus, early-replicating foci, markers of R-bands, are localized in the peripheral chromatin halo, whereas late-replicating foci, corresponding to G-bands, remain associated with the axial regions of chromatids. Remarkably, despite these major changes in the structure of the chromosomal bands, the replication foci still preserve their discrete structure.

Animals↗