Dependence of Z-DNA antibody binding to polytene chromosomes on acid fixation and DNA torsional strain

There is considerable interest in the existence and significance of alternative conformations of DNA to the right-handed B-form described originally by Watson and Crick. The indirect immunofluorescence observations of Nordheim et al., Arndt-Jovin et al. and Lemeunier et al. that antibodies against left-handed Z-DNA bind to polytene chromosomes have thus assumed considerable importance. However, there is a paradox: some workers observe Z-DNA in interbands and others in bands. We report here that binding of Z-DNA antibodies to Drosophila polytene chromosomes prepared without acid fixation is at background level, and that following acid fixation the same antibody treatment leads to intense fluorescence. Depending on the extent of exposure to 45% acetic acid, fluorescence can occur primarily in interbands or in bands. Furthermore, antibody binding is dependent on elastic torsional strain in the DNA molecules.     

泸定百合根尖染色体C-带分析

利用Giemsa C-带方法对泸定百合(Lilium sargentiae Wilson)进行了研究.结果表明:泸定百合的染色体数目为2n=24,每条染色体都显示出了可以明显区别的特征带;强带主要集中在染色体的着丝粒区域,在长短臂上也显示出可以相互识别的深浅不一的带纹.通过Giemsa C-带方法可以将泸定百合的每条染色体区分开.     

Effect of novobiocin on initiation of DNA replication in Bacillus subtilis.

The initiation of DNA replication of small replicons in vitro involves conformational changes in the whole DNA molecule or in the region near to the replication origin. One striking finding has been the role of DNA gyrase (that is, the necessity for supercoiled structure) in the initial stage of ColE1 replication in vitro. However, little is known about the effect of gyrase on the initiation of replication of bacterial chromosomes in vivo. We have constructed a map of cleavage sites of restriction enzymes at the region of the origin of replication of the Bacillus subtilis chromosome (accompanying paper). This has now enabled us to examine the effect of novobiocin, a selective inhibitor of DNA gyrase, on the replication of the specific chromosomal segments near the origin and to seek a possible role for the gyrase in the initiation of chromosomal replication. We have found that only a limited segment of the chromosome at the origin region was replicated in the presence of novobiocin. This effect allowed us to locate the site of the origin of replication to within a DNA fragment of molecular weight 3.4 x 10(6).     

济南花鸡染色体研究

对山东省培育的家鸡优良品种济南花鸡的三个品系：草花鸡、麻花鸡和无翼鸡作了染色体核型分析，进行了染色体的显带处理，探讨了Ｇ－、Ｃ－带型和核仁组织者的分布，并进行了比较研究．     

Spontaneous excision of a large composite transposable element of Drosophila melanogaster

The TE1 family of transposable elements (TEs) of Drosophila consists of unusually large transposons, cytologically visible in larval polytene chromosomes as one or more bands. They are composite elements, as their termini consist of foldback (FB) sequences which are themselves transposable. The location of FB elements at the termini of transposable elements suggests that these sequences have a direct role in the genetic instability of TEs. To investigate the structural and phenotypic consequence of TE excision, we have cloned genomic DNA required for the expression of the no-ocelli (noc) gene of Drosophila; this gene has been mutated by the insertion of TE146, a member of the TE1 family carrying six polytene chromosome bands including functional copies of the white (w+) and roughest (rst+) genes. As reported here, our experiments indicate that the spontaneous excision of TE146, which results in the loss of the w+ and rst+ markers, can occur either as a single-step event or following a partial internal deletion. In either case, the end product is an imprecise excision in which a residual portion of the element, varying in size from 3 to 10 kilobases (kb), is left at the insertion site. These residual sequences share homology with the FB family. Furthermore, despite their imprecise nature, all these spontaneous excisions restore a wild-type noc+ phenotype.     

两种鱼的复制带显带研究

采用活体直接注射ＢｒｄＵ的方法,对黄颡鱼和鲶鱼的染色体复制带进行了研究．结果发现,采用ＢｒｄＵ－Ｈｏｅｃｈｓｔ－Ｇｉｅｍｓａ方法,获得了这两种鱼的复制带图像,带纹清晰稳定．复制带可分早、中、晚三个时期,从早期到晚期,带纹逐渐减少;常染色质早复制,异染色质晚复制,复制中期可看到着丝粒区、端粒区和居间区,其中特别是ＮＯＲｓ处浅染．根据试验结果,对鱼类染色体的复制带特征进行了讨论     

Cloning defined regions of the human genome by microdissection of banded chromosomes and enzymatic amplification

The molecular analysis of many genetic diseases requires the isolation of probes for defined human chromosome regions. Existing techniques such as the screening of chromosome-specific libraries, subtractive DNA cloning and chromosome jumping are either tedious or not generally applicable. Microdissection and microcloning has successfully been applied to various chromosome regions in Drosophila and mouse, but conventional microtechniques are too coarse and inefficient for analysis of the human genome. Because microdissection has previously been used on unbanded chromosomes only, cell lines in which the chromosome of interest could be identified without banding had to be used. At least one hundred chromosomes were needed for dissection and lambda vectors used to achieve maximum cloning efficiency. Recombinant phage clones are, however, more difficult to characterize than plasmid clones. Here we describe the dissection of the Langer-Giedion syndrome region on chromosome 8 from GTG-banded metaphase chromosomes (G-banding with trypsin-Giemsa) and the universal enzymatic amplification of the dissected DNA. Eighty per cent of clones from this library (total yield 20,000) identify single-copy DNA sequences. Fifty per cent of clones detect deletions in two patients with Langer-Giedion syndrome. Although the other clones have not yet been mapped, this result demonstrates that thousands of region-specific probes can be isolated within ten days.     

阿拉拉特小麦染色体的C-带和N-带分析

应用Ｃ－分带和喧技术对阿拉拉特小麦（Ｔｒｉｔｉｃｒｍ ａｒａｒａｔｉｃｕｍ Ｊａｋｕｂｚ,２ｎ＝２８,Ａ＾ｂＡ＾ｂＧＧ）的根尖细胞进行染色体构成分析,结果分析,结果表明：（１）Ｃ－分带和Ｎ－分带方法均可以使阿拉拉特不麦染色体显示稳定带型;（２）根据带型可以明确区分阿拉拉特不麦各条染色体;（３）阿拉拉特小麦Ａ、Ｇ组染色体带型与普通小麦Ａ、Ｂ组染色体带型差异明显,利用分带方法可以区分阿拉拉特小麦与普通     

野生二粒小麦的Giemsa C带核型

采用改良C带技术对野生二粒小麦根尖细胞染色体进行了分带研究结果表明：野生二粒小麦体细胞中有14对染色体，染色体组型AABB不同染色体上带的数目、大小、强弱及分布情况各异，而同源染色体的带型一致，根据C带带型特征很容易将野生二粒小麦不同染色体组、及不同染色体分开因此，C带可作为野生二粒小麦的细胞学标记．此外，除4B染色体外，野生二粒小麦染色体的C带带型特征与普通小麦相应染色体相似，这从染色体结构方面进一步证实了野生二粒小麦是普通小麦祖先种之一的假设     

Conservation and change in the DNA sequences coding for alcohol dehydrogenase in sibling species of Drosophila

The DNA sequences of the alcohol dehydrogenase (Adh) genes of four very closely related species of Drosophila show that the rates of nucleotide change vary greatly in different functional domains of this gene. A phylogeny of these species based on the Adh sequence data is consistent with that based on polytene chromosome banding patterns.     

Three-dimensional architecture of a polytene nucleus

The three-dimensional chromosome topography in an intact nucleus has been determined using fluorescently stained Drosophila polytene chromosomes, optical fluorescence microscopy and newly developed, generally applicable, cellular image reconstruction techniques. The folding pattern is a complex mixture of parallel chromosomal segments and intertwined coils and shows extensive interaction of the chromosomes with the nuclear envelope.     

Telomeric repeat from T. thermophila cross hybridizes with human telomeres

The ends (telomeres) of eukaryotic chromosomes must have special features to ensure their stability and complete replication. Studies in yeast, protozoa, slime moulds and flagellates show that telomeres are tandem repeats of simple sequences that have a G-rich and a C-rich strand. Mammalian telomeres have yet to be isolated and characterized, although a DNA fragment within 20 kilobases of the telomeres of the short arms of the human sex chromosomes has been isolated. Recently we showed that a chromosome from the fission yeast Schizosaccharomyces pombe could, in some cases, replicate as an autonomous mini-chromosome in mouse cells. By extrapolation from other systems, we reasoned that mouse telomeres could be added to the S. pombe chromosome ends in the mouse cells. On setting out to test this hypothesis we found to our surprise that the telomeric probe used (containing both the S. pombe and Tetrahymena thermophila repeats) hybridized to a series of discrete fragments in normal mouse DNA and DNA from a wide range of eukaryotes. We show here that the sequences hybridizing to this probe are located at the telomeres of most, if not all, human chromosomes and are similar to the Tetrahymena telomeric-repeat component of the probe.     

日本黄脊蝗的核型和C─带带型

采用涂片法和ＢＳＧ技术研究了日本黄脊蝗（Ｐａｌａｎｇａｊａｐｏｎｃａ）的核型和Ｃ─带带型。结果表明：核型属常见核型；２３条染色体均显着丝粒带，其中６对中、小染色体还显示了端带；结构异染色质较多地分布于这６对染色体。精原细胞有丝分裂中期和初级精母细胞减数分裂后期工的染色体在核型，带型上基本一致。     

日本黄脊蝗的核型和C─带带型

采用涂片法和ＢＳＧ技术研究了日本黄脊蝗（Ｐａｌａｎｇａｊａｐｏｎｃａ）的核型和Ｃ─带带型。结果表明：核型属常见核型；２３条染色体均显着丝粒带，其中６对中、小染色体还显示了端带；结构异染色质较多地分布于这６对染色体。精原细胞有丝分裂中期和初级精母细胞减数分裂后期工的染色体在核型，带型上基本一致。     

Chromosome length influences replication-induced topological stress

During chromosome duplication the parental DNA molecule becomes overwound, or positively supercoiled, in the region ahead of the advancing replication fork. To allow fork progression, this superhelical tension has to be removed by topoisomerases, which operate by introducing transient DNA breaks. Positive supercoiling can also be diminished if the advancing fork rotates along the DNA helix, but then sister chromatid intertwinings form in its wake. Despite these insights it remains largely unknown how replication-induced superhelical stress is dealt with on linear, eukaryotic chromosomes. Here we show that this stress increases with the length of Saccharomyces cerevisiae chromosomes. This highlights the possibility that superhelical tension is handled on a chromosome scale and not only within topologically closed chromosomal domains as the current view predicts. We found that inhibition of type I topoisomerases leads to a late replication delay of longer, but not shorter, chromosomes. This phenotype is also displayed by cells expressing mutated versions of the cohesin- and condensin-related Smc5/6 complex. The frequency of chromosomal association sites of the Smc5/6 complex increases in response to chromosome lengthening, chromosome circularization, or inactivation of topoisomerase 2, all having the potential to increase the number of sister chromatid intertwinings. Furthermore, non-functional Smc6 reduces the accumulation of intertwined sister plasmids after one round of replication in the absence of topoisomerase 2 function. Our results demonstrate that the length of a chromosome influences the need of superhelical tension release in Saccharomyces cerevisiae, and allow us to propose a model where the Smc5/6 complex facilitates fork rotation by sequestering nascent chromatid intertwinings that form behind the replication machinery.     

DNA breaks and chromosome pulverization from errors in mitosis

The involvement of whole-chromosome aneuploidy in tumorigenesis is the subject of debate, in large part because of the lack of insight into underlying mechanisms. Here we identify a mechanism by which errors in mitotic chromosome segregation generate DNA breaks via the formation of structures called micronuclei. Whole-chromosome-containing micronuclei form when mitotic errors produce lagging chromosomes. We tracked the fate of newly generated micronuclei and found that they undergo defective and asynchronous DNA replication, resulting in DNA damage and often extensive fragmentation of the chromosome in the micronucleus. Micronuclei can persist in cells over several generations but the chromosome in the micronucleus can also be distributed to daughter nuclei. Thus, chromosome segregation errors potentially lead to mutations and chromosome rearrangements that can integrate into the genome. Pulverization of chromosomes in micronuclei may also be one explanation for 'chromothripsis' in cancer and developmental disorders, where isolated chromosomes or chromosome arms undergo massive local DNA breakage and rearrangement.     

Mouse Karyotype Obtained by Combining DAPI Staining with Image Analysis

In this study, mitotic metaphase chromosomes in mouse were identified by a new chromosome fluorescence banding technique combining DAPI staining with image analysis. Clear 4＇, 6-diamidino-2-phenylindole （DAPI） multiple bands like （J-hands could be produced in mouse. The Meta- Morph software was then used to generate linescans of pixel intensity for the banded chromosomes from short arm to long arm. These linescans were sufficient not only to identify each individual chromosome but also analyze the physical sites of bands in chromosome. Based on the results, the clear and accurate karyotype of mouse metaphase chromosomes was established. The technique is therefore considered to he a new method for cytological studies of mouse.     

泽蛙(Rana l.limnocharis)染色体高分辨带型初步分析

本文用简化的高分辨显带方法,直接将5——溴脱氧尿嘧啶核苷(Brdu)注射到泽蛙体内,替代胸腺嘧啶脱氧核苷(TdR)渗入正在复制的DNA中,干扰染色体三级结构,使染色体伸长,从而获得了大量带纹清晰、丰富的早中期、中期染色体,并成功地进行了高分辨带型分析。结果和衡红强等、赵亚力用外周血淋巴细胞培养制备的黑斑蛙,绿臭蛙染色体高分辨带型一致。