Chromosome

About: Chromosome is a research topic. Over the lifetime, 17538 publications have been published within this topic receiving 660077 citations. The topic is also known as: chromosomes & GO:0005694.

Chromosomal localization of human β globin gene on human chromosome 11 in somatic cell hybrids

Abstract: We have successfully used a DNA·cDNA molecular hybridization assay to directly determine the presence or absence of human β globin gene sequences in 20 human—mouse somatic cell hybrids, each of which contained a different subset of human chromosomes. The assay is specific for the individual human globin genes and will detect the presence of a globin gene if the relevant chromosome is present in only 10% of the cells of a hybrid population. The content of human chromosomes in each hybrid clone was characterized by Giemsa 11 staining, Giemsa trypsin-Hoechst 33258 staining, and by the use of 22 independent isozyme markers for 17 different human chromosomes. All human chromosomes were present in one or more cell lines devoid of the human β globin gene except for 6, 8, 9, 11, and 13. Among these latter chromosomes, only chromosome 11 was present in the six hybrid clones that contained the human β globin gene. In fact, chromosome 11 was the only human chromosome that was present in all of the six hybrid clones found to be positive for the human β globin gene. Two sister clones, 157-BNPT-1 and 157-BNPT-4, had similar subsets of human chromosomes except that 11 was present only in 157-BNPT-4. 157-BNPT-4 contained the human β globin gene while 157-BNPT-1 did not. DNA from three hybrid lines was also annealed to purified human γ globin cDNA; two lines positive for human β globin gene sequences also contained human γ globin gene sequences while one line was negative for both β and γ gene sequences. On the basis of these results, the human β and γ globin genes have been assigned to human chromosome 11.

The nucleotide and deduced amino acid sequences of an HMW glutenin subunit gene from chromosome 1B of bread wheat ( Triticum aestivum L.) and comparison with those of genes from chromosomes 1A and 1D

Abstract: The nucleotide and deduced amino acid sequences of a high molecular weight glutenin subunit gene derived from chromosome 1B of bread wheat (Triticum aestivum L) are reported The encoded protein corresponds to the y-type subunit 1B9 Comparison of the 5′ upstream untranslated regions of this gene and a previously reported silent y-type gene derived from chromosome 1A showed a deletion of 85 bp in the latter A sequence present in this region of the 1By 9 gene shows homology with part of the “-300 element” which is conserved in the 5′ upstream regions of other prolamin genes from barley, wheat and maize (Forde BG et al 1985) It is suggested that the absence of this element is responsible for the lack of expression of the 1Ay gene Comparison of the derived amino acid sequence with those reported previously for the silent 1Ay gene and the expressed x-type (1Dx2) and y-type (1Dy12) genes derived from chromosome 1D showed that the three y-type proteins are closely related In contrast the x-type subunit (1Dx2) shows clear differences in the N-terminal region and in the number, type and organisation of repeats in the central repetitive domain

Genetic evidence that EBNA-1 is needed for efficient, stable latent infection by Epstein-Barr virus

Abstract: The life cycle of Epstein-Barr virus (EBV) appears to depend upon a mechanism to replicate and maintain the viral genome in an autonomous state in expanding B-cell populations during the initial phase of latency (20–22). Maintenance of the viral chromosome in proliferating cells required that it be duplicated each cell cycle and passed on to daughter nuclei during mitosis. During latent infection, the circularized EBV genome replicates during the S phase of the cell cycle (14), apparently under a cellular control mechanism that limits each viral chromosome to one round of replication per S phase (1, 47). EBV chromosomes associate with the condensed cellular chromosomes during mitosis, ensuring that all copies of the EBV chromosome are enveloped within daughter nuclei as they form at the close of mitosis (15). An 1,800-bp region of the EBV genome, oriP, was identified based on its ability to confer long-term maintenance of recombinant plasmids under selection in human cell lines (44). oriP requires only a single EBV-encoded protein, EBNA-1, for this activity (31, 48). oriP provides both replication and segregation functions to plasmids that carry it through two distinct and essential functional elements (4, 35), both of which bind EBNA-1 at multiple sites (34). A cluster of four EBNA-1 binding sites, usually called the DS for a dyad symmetry element contained within it, supports plasmid replication (42) and is the point from which replication forks diverge in both directions, at least within a few hundred base pairs, the resolution achieved by a two-dimensional gel analysis of replication intermediates (9). The other essential element of oriP is a repetitive array of EBNA-1 binding sites, a family of 30-bp repeats called the FR, which is located nearly 1 kb away from the DS. The FR supports very little plasmid replication by itself, but in the presence of EBNA-1, it allows plasmids to be retained with their genes active for prolonged periods of time after being introduced into cells (23, 35). It was shown that oriP could confer mitotic stability to a 600-kb, circularized, cloned segment of a human chromosome in cells containing EBNA-1 and cause the artificial plasmid to associate with condensed human chromosomes during mitosis (36). EBNA-1 itself associates with human metaphase chromosomes (12) and also has the capacity to link together DNA molecules to which it is bound, by self-interaction (8, 32, 38). The mechanism behind the plasmid retention function of the FR and EBNA-1 is therefore likely to involve EBNA-1-mediated tethering of plasmids to human chromosomes during mitosis to prevent their loss to the cytoplasm. It has long been assumed that oriP and EBNA-1 are together responsible for supporting the replication and maintenance of the circular EBV chromosome during latent infection of mitotically active cells, but a direct test of this has been lacking. However, in recent years, evidence has accumulated to suggest that the replication initiation function of oriP is dispensable to EBV. Two-dimensional gel analysis of replication intermediates has indicated that on the EBV chromosome, oriP is replicated passively from distant origins most of the time, with initiation occurring within oriP only a fraction of the time (29). An isolate of the cell line X50-7 was found to carry a variant EBV genome which had sustained a deletion that removed all of oriP except for the FR (43); when tested on plasmids, the FR does not support significant replication in the absence of the DS of oriP (4, 31, 35, 42, 44). Recent genetic studies in this laboratory have confirmed that the DS of oriP can be deleted from EBV without seriously compromising its ability to maintain its chromosome autonomously during latent infection (our unpublished data). Could the viral chromosomal maintenance function, or segregation function, of EBNA-1 and oriP be redundant, too? EBNA-1 and oriP have been conserved during the evolution of the close relatives of EBV that infect Old World primates (6, 30, 46). However, the FR of oriP is also a potent EBNA-1-dependent enhancer of transcription, and EBNA-1 and the FR appear to be important for proper transcription from two EBV promoters that give rise to expression of genes required to immortalize B cells (10, 33, 39). Among the more distantly related gamma herpesviruses that are known to support autonomous replication of their viral genomes during latent infection, none appears to have a homolog of EBNA-1 or of oriP (2, 5, 24, 40). It therefore seemed possible that the plasmid maintenance property of EBNA-1 and oriP could be functionally redundant, like the replication initiation function. To test the importance of EBNA-1 for latent infection by EBV, we introduced a frameshift mutation into the EBNA-1 gene of EBV by homologous recombination. Viruses carrying this mutation could not immortalize B cells nor stably infect an EBV-negative B-cell line. This suggests that the chromosome maintenance function of EBNA-1 and oriP is required for efficient and stable latent infection.

Analysis of chromosome positions in the interphase nucleus of Chinese hamster cells by laser-UV-microirradiation experiments.

Abstract: Unsynchronized cells of an essentially diploid strain of female Chinese hamster cells derived from lung tissue (CHL) were laser-UV-microirradiated (λ=257 nm) in the nucleus either at its central part or at its periphery. After 7–9 h postincubation with 0.5 mM caffeine, chromosome preparations were made in situ. Twenty-one and 29 metaphase spreads, respectively, with partial chromosome shattering (PCS) obtained after micro-irradiation at these two nuclear sites, were Q-banded and analyzed in detail. A positive correlation was observed between the frequency of damage of chromosomes and both their DNA content and length at metaphase. No significant difference was observed between the frequencies of damage obtained for individual chromosomes at either site of microirradiation. The frequency of joint damage of homologous chromosomes was low as compared to nonhomologous ones. Considerable variation was noted in different cells in the combinations of jointly shattered chromosomes. Evidence which justifies an interpretation of these data in terms of an interphase arrangement of chromosome territories is discussed. Our data strongly argue against somatic pairing as a regular event, and suggest a considerable variability of chromosome positions in different nuclei. However, present data do not exclude the possibility of certain non-random chromosomal arrangements in CHL-nuclei. The interphase chromosome distribution revealed by these experiments is compared with centromere-centromere, centromere-center and angle analyses of metaphase spreads and the relationship between interphase and metaphase arrangements of chromosomes is discussed.

Chromosome-Specific Painting in Cucumis Species Using Bulked Oligonucleotides.

Abstract: Chromosome-specific painting is a powerful technique in molecular cytogenetic and genome research. We developed an oligonucleotide (oligo)-based chromosome painting technique in cucumber (Cucumis sativus) that will be applicable in any plant species with a sequenced genome. Oligos specific to a single chromosome of cucumber were identified using a newly developed bioinformatic pipeline and then massively synthesized de novo in parallel. The synthesized oligos were amplified and labeled with biotin or digoxigenin for use in fluorescence in situ hybridization (FISH). We developed three different probes with each containing 23,000-27,000 oligos. These probes spanned 8.3-17 Mb of DNA on targeted cucumber chromosomes and had the densities of 1.5-3.2 oligos per kilobases. These probes produced FISH signals on a single cucumber chromosome and were used to paint homeologous chromosomes in other Cucumis species diverged from cucumber for up to 12 million years. The bulked oligo probes allowed us to track a single chromosome in early stages during meiosis. We were able to precisely map the pairing between cucumber chromosome 7 and chromosome 1 of Cucumis hystrix in a F1 hybrid. These two homeologous chromosomes paired in 71% of prophase I cells but only 25% of metaphase I cells, which may provide an explanation of the higher recombination rates compared to the chiasma frequencies between homeologous chromosomes reported in plant hybrids.