A family of related sequences associated with (TTTAGGG)n repeats are located in the interstitial regions of wheat chromosomes

A family of related sequences associated with (TTTAGGG) _n repeats has been cloned from the wheat cultivar Chinese Spring. These sequences reveal a high level of polymorphism between wheat varieties when used as restriction fragment length polymorphism (RFLP) probes. Although this family of sequences contains motifs homologous to the repeats in the telomeres of wheat, they are located at interstitial sites on wheat chromosomes.     

A family of endosperm globulins encoded by genes located in group 1 chromosomes of wheat and related species

Summary A new group of proteins soluble in salt solutions and organic solvents (70% ethanol and chloroform-methanol mixtures), but not in water, has been isolated from wheat and rye endosperm. The molecular weights (23–26 kDa) and amino acid compositions of the different fractions characterized suggest a high degree of homology among the major components of the fractions in wheat and rye. Compensating nulli-tetrasomic and ditelosomic lines of hexaploid wheat have been analysed by two-dimensional electrophoresis and genes for these proteins have been assigned to the short arms of chromosomes 1 A, 1 B and 1 D. A similar analysis of Triticum aestivum/Secale cereale and T. aestivum/Agropyron elongatum addition and substitution lines has shown that genes for the corresponding globulins are located in the short arms of group 1 chromosomes of these species.     

Telomeric repeat [TTAGGG]n sequences of human chromosomes are conserved in chimpanzee (Pan troglodytes)

Summary Using a series of genetic parameters, attempts have been made for more than two decades to establish the close kinship of human (Homo sapiens) with chimpanzee (Pan troglodytes). Molecular and cytogenetic data presently suggest that the two species are closely related. The recent isolation of a human telomeric probe (P5097-B.5) has prompted us to cross hybridize it to chimpanzee chromosomes in order to explore convergence and/or divergence of the telomeric repeat sequences (TTAGGG)_n. On hybridization, the human probe bound to both ends (telomeres) of chimpanzee chromosomes, suggesting a concerted evolution of tandemly repeated short simple sequences (TTAGGG)_n. Even the terminal heterochromatin of chimpanzee chromosomes was found to be endowed with telomeric repeats, suggesting that evolution of heterochromatin and capping with tandemly repeated short sequences are highly complex phenomena.     

The repeated sequences (incB) preceding the protein E gene of plasmid mini-F are essential for replication

Summary At the XhoI site (45.08F) of plasmid mini-F a deletion of 649 bp was generated employing exonuclease Bal31. By this deletion nucleotide sequences functioning as origin II and the four 19 bp direct repeats constituting the incB region in front of the E protein gene were removed from the plasmid. Analysis of proteins radioactively labelled in Escherichia coli mini-cells indicated that all mini-F encoded proteins are expressed. However, the plasmid carrying the deletion was not capable of replicating from the primary origin (origin I, 42.6F). Recently a smaller deletion at the XhoI site (45.08F) of about 300 bp, removing only the region functioning as origin II and replicating from origin I, was described by Tanimoto and Iino (1984, 1985). The data presented suggest that the incB repeats are essential for the initiation of replication from origin I, and possibly also from origin II, and seem not to be engaged in the autoregulation of E protein expression.     

Absence of repetitive DNA sequences associated with sex chromosomes in natural populations of the Trinidad guppy (Poecilia reticulata)

The genus Poecilia has been widely studied as a model for the evolution of sex chromosomes. In the course of molecular studies on population genetic structure and sexual selection in the Trinidad guppy, we examined our preparations for male-linked, repetitive DNA polymorphisms. We have not obtained any evidence of male-specific polymorphisms, in contrast to an earlier study. Our results have significant implications for theories on the evolution of sex chromosomes.Correspondence to: F. Breden     

Pausing of simian virus 40 DNA replication fork movement in vivo by (dG-dA)n·(dT-dC)n tracts

We have earlier demonstrated that a sequence bordering an amplified DNA segment and containing the unusual sequence (dG-dA)_n·(dT-dC)_n could slow replication fork movement [Rao et al., Nucleic Acids Res. 16 (1988) 8077–8094]. This was done by cloning the unusual sequence in simian virus 40 (SV40) and following the rate of incorporation of radioactively labeled nucleotides into various regions of the SV40 genome. In the present study, we have analyzed the in vivo replicative intermediates of the SV40 variants containing the unusual sequences by a two-dimensional gel electrophoretic technique. We found that the technique can be used to detect minor pauses in DNA replication and demonstrated that the cloned (dG-dA)_n·(dT-dC)_n tracts, that can potentially adopt triplex structures, could slow DNA replication fork movement. A sequence from the plasmid pUC18 did not slow fork movement when cloned in the same locus of SV40. The pause caused by the alternating guanosine-adenosine repeats might play a role in the regulation of DNA replication and gene amplification in vivo.     

Mapping loci associated with flour colour in wheat (Triticum aestivum L.)

 An RFLP map constructed using 150 single seed descent (SSD) lines from a cross between two hexaploid wheat varieties (‘Schomburgk’בYarralinka’) was used to identify loci controlling flour colour. Flour colour data were obtained from field trials conducted over two seasons at different sites. The estimated heritability of this trait was calculated as 0.67. Two regions identified in the preliminary analysis on chromosomes 3A and 7A, accounted for 13% and 60% of the genetic variation respectively. A detailed analysis of the major locus on 7A was conducted through fine mapping of AFLP markers identified using bulked segregant analysis (BSA). Seven additional markers were identified by the BSA and mapped to the region of the 7A locus. The applicability of these markers to identify wheat lines with enhanced flour colour is discussed. Received: 30 September 1997 / Accepted: 4 February 1998     

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

Summary 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.     

The organization of macronuclear DNA sequences associated with C4A4 repeats in the polytene chromosomes of Stylonychia lemnae

Gene libraries of the micronucleus and the macronuclear anlagen of the polytene chromosome stage of Stylonychia lemnae were screened for internal C₄A₄ repeats. The number of these internal repeats was shown to be identical in both kinds of nuclei. Analysis of macronuclear sequences associated with C₄A₄ in the polytene chromosomes showed that several macronuclear DNA sequences are clustered. However, interspersed between short exons of one gene are located exons of several other genes, i.e. the exon of one gene is an intron for several other genes.by M. Trendelenburg     

Simple repetitive sequences are associated with differentiation of the sex chromosomes in the guppy fish

Summary Hybridization of restriction enzymedigested genomic guppy (Poecilia reticulata, Poeciliidae) DNA with the oligonucleotide probe (GACA)₄ revealed a male-specific simple tandem repeat locus, which defines the Y chromosome in outbred populations. The related (GATA)₄ probe identifies certain males with the red color phenotype. In contrast only in two out of eight laboratory guppy strains was the typical (GACA)₄ band observed. By specific staining of the constitutive heterochromatin one pair of chromosomes could also be identified as the sex chromosomes, confirming the XX/XY mechanism of sex determination. All males exhibit Y chromosomes with a large region of telomeric heterochromatin. Hybridization in situ with nonradioactively labeled oligonucleotide probes localized the (GACA)_n repeats to this heterochromatic portion. Together these results may be regarded as a recent paradigm for the differentiation of heteromorphic sex chromosomes from a pair of autosomes during the course of evolution. According to the fish model system, this may have happened in several independent consecutive steps.     

A novel repetitive sequence associated with the centromeric regions of Arabidopsis thaliana chromosomes

 The middle repetitive fraction of the Arabidopsis genome has been relatively poorly characterized. We describe here a novel repetitive sequence cloned in the plasmid mi167, and present in ∼90 copies in the genome of Arabidopsis thaliana ecotype Columbia. Hybridization analysis to physically mapped YAC clones representing Arabidopsis chromosome 4 revealed four mi167-hybridizing loci, all clustered near the centromere. No other loci were detected on YAC clones covering chromosome 4. In situ hybridisation experiments to Arabidopsis chromosome spreads showed that mi167-hybridizing sequences are clustered at the centromeric heterochromatin of all five chromosomes; on two chromosomes the hybridization appeared to be localised on one arm. Additional mi167-hybridizing loci were detected, one of which was adjacent to a non-centromeric, heterochromatic region. This work supports the idea that the majority of middle repetitive DNA in the Arabidopsis genome is clustered. It also adds to our understanding of the organization of the centromere of Arabidopsis chromosome 4. Received: 19 February 1996 / Accepted: 30 June 1996     

The haemochromatosis candidate gene HFE (HLA-H) of man and mouse is located in syntenic regions within the histone gene cluster

The HFE (HLA-H) gene is a strong candidate gene for hereditary haemochromatosis and was localized on the short arm of chromosome 6 to 6p21.3-p22. In addition, the sequence of the homologous mouse and rat cDNA and a partial sequence from the mouse gene have been reported recently. In this report, we describe the location of the human and the mouse HFE (HLA-H) gene within the histone gene clusters on the human chromosome 6 and the mouse chromosome 13. Both the human and the murine gene were located on syntenic regions within the histone gene clusters in the vicinity of the histone H1t gene. The genomic sequence of the human HFE (HLA-H) gene and the 3′ portion of the homologous mouse gene were determined. Comparison of the genomic sequences from man and mouse and the cDNA sequence from rat shows significant similarities, also beyond the transcribed region of the mouse gene. J. Cell. Biochem. 69:117–126, 1998. © 1998 Wiley-Liss, Inc.     

Long poly(A) tracts in the human genome are associated with the Alu family of repeated elements

Long poly(dA).poly(dT) tracts (poly(A) tracts), regions of DNA containing at least 20 contiguous dA residues on one strand and dT residues on the complementary strand, are found in about 2 X 10(4) copies interspersed throughout the human genome. Using poly(dA).poly(dA) as a hybridization probe, we identified recombinant lambda phage that contained inserts of human DNA with poly(A) tracts. Three such tracts have been characterized by restriction mapping and sequence analysis. One major poly(A) tract is present within each insert and is composed of from 28 to 35 A residues. In each case, the poly(A) tract directly abuts the 3' end of the human Alu element, indicating that the major class of poly(A) tracts in the human genome is associated with this family of repeats. The poly(A) tracts are also adjacent to A-rich sequences and, in one case, to a polypurine tract, having the structure GA3-GA3-GA4-GA6-GA5-GA4. We suggest that repetitive cycles of unequal crossing over may give rise to both the long poly(A) and polypurine tracts observed in this study.     

Chromosomal distribution of interstitial telomeric sequences as signs of evolution through chromosome fusion in six species of the giant water bugs (Hemiptera,Belostoma)

Tandem arrays of TTAGG repeats show a highly conserved location at the telomeres across the phylogenetic tree of arthropods. In giant water bugs Belostoma, the chromosome number changed during speciation by fragmentation of the single ancestral X chromosome, resulting in a multiple sex chromosome system. Several autosome–autosome fusions and a fusion between the sex chromosome pair and an autosome pair resulted in the reduced number in several species. We mapped the distribution of telomeric sequences and interstitial telomeric sequences (ITSs) in Belostoma candidulum (2n = 12 + XY/XX; male/female), B. dentatum (2n = 26 + X₁X₂Y/X₁X₁X₂X₂), B. elegans (2n = 26 + X₁X₂Y/X₁X₁X₂X₂), B. elongatum (2n = 26 + X₁X₂Y/X₁X₁X₂X₂), B. micantulum (2n = 14 + XY/XX), and B. oxyurum (2n = 6 + XY/XX) by FISH with the (TTAGG)_n probes. Hybridization signals confirmed the presence of TTAGG repeats in the telomeres of all species examined. The three species with reduced chromosome numbers showed additional hybridization signals in interstitial positions, indicating the occurrence of ITS. From the comparison of all species here analyzed, we observed inverse relationships between chromosome number and chromosome size, and between presence/absence of ITS and chromosome number. The ITS distribution between these closely related species supports the hypothesis that several telomere–telomere fusions of the chromosomes from an ancestral diploid chromosome number 2n = 26 + XY/XX played a major role in the karyotype evolution of Belostoma. Consequently, our study provide valuable features that can be used to understand the karyotype evolution, may contribute to a better understanding of taxonomic relationships, and also elucidate the high plasticity of nuclear genomes at the chromosomal level during the speciation processes.     

Human acyl-coenzyme A:cholesterol acyltransferase 1 (acat1) sequences located in two different chromosomes (7 and 1) are required to produce a novel ACAT1 isoenzyme with additional sequence at the N terminus

A rare form of human ACAT1 mRNA, containing the optional long 5'-untranslated region, is produced as a 4.3-kelonucleotide chimeric mRNA through a novel interchromosomal trans-splicing of two discontinuous RNAs transcribed from chromosomes 1 and 7. To investigate its function, we express the chimeric ACAT1 mRNA in Chinese hamster ovary cells and show that it can produce a larger ACAT1 protein, with an apparent molecular mass of 56 kDa on SDS-PAGE, in addition to the normal, 50-kDa ACAT1 protein, which is produced from the ACAT1 mRNAs without the optional long 5'-untranslated repeat. To produce the 56-kDa ACAT1, acat1 sequences located at both chromosomes 7 and 1 are required. The 56-kDa ACAT1 can be recognized by specific antibodies prepared against the predicted additional amino acid sequence located upstream of the N-terminal of the ACAT1(ORF). The translation initiation codon for the 56-kDa protein is GGC, which encodes for glycine, as deduced by mutation analysis and mass spectrometry. Similar to the 50-kDa protein, when expressed alone, the 56-kDa ACAT1 is located in the endoplasmic reticulum and is enzymatically active. The 56-kDa ACAT1 is present in native human cells, including human monocyte-derived macrophages. Our current results show that the function of the chimeric ACAT1 mRNA is to increase the ACAT enzyme diversity by producing a novel isoenzyme. To our knowledge, our result provides the first mammalian example that a trans-spliced mRNA produces a functional protein.     

Proteins with tandemly arranged repeats of a highly charged 16-amino-acid motif encoded by the Dhmst101 gene family are structural components of the outer sheath of the extremely elongated sperm tails of Drosophila hydei

Fruit fly species of the genus Drosophila show a remarkable variation in sperm length. Some of them produce gigantic sperm several times the total male body length. Sperm of Drosophila hydei, for example, are more than 20 mm long. Little is known about the advantage of such elongated sperm or about the proteins that stabilize their thin flagellar tails. Recently, two members of a novel gene family Dhmst101(1) and Dhmst101(2), whose gene products are associated with the sperm tail, were isolated and characterized. Here a third member of this gene family, Dhmst101(3), is described. It was previously demonstrated that all three genes are located in a single small cluster on chromosome 5 of D. hydei. They are located within 15 kb of genomic DNA, oriented in the same direction and transcribed testis-specifically. The encoded sperm tail-specific proteins are mainly composed of tandemly arranged repeats of a highly charged, cysteine-containing motif of 16 amino acids with the consensus sequence KKKCA/EEAAKKEKEAAE. Experiments with synthetic repeat monomers and dimers have demonstrated a tendency for alpha-helical rod formation, which increased strongly with an increase in repeat number. Therefore, Dhmst101 proteins with 7-60 repeats with regularly spaced cystein-residues are thus expected to form long alpha-helical rods cross-linked by numerous Cys-Cys bridges. Here we apply immunoelectron microscopy and monospecific antibodies, alpha-mst101, raised against the KKKCAEAAKKEKEAAE-motif to investigate the distribution of Dhmst101 proteins within the sperm tail of D. hydei. We show that Dhmst101 proteins are part of the outer sheath of the sperm tail where they presumably help to provide a tight but elastic envelope for the extremely extended spermatozoa of D. hydei.     

A subset of the elements of the 1731 retrotransposon family are preferentially located in regions of the Y chromosome that are polytenized in larval salivary glands of Drosophila melanogaster

It has been previously reported that the abundance and distribution of transposable elements (TEs) in Drosophila heterochromatin are conserved in unrelated stocks although they may greatly differ between families. The biases in genomic distribution of TEs are potentially informative for understanding host–transposon interactions. Here we report that in most stocks, one to four elements of the 1731 retrotransposon family are located on the Y chromosome within regions that appear to be polytenized in larval salivary glands. We discuss the hypothesis that these elements may be beneficial to the host and consider the relevance of our observations to the organization of sequences within the heterochromatin.     

Genus-specific localization of the TaiI family of tandem-repetitive sequences in either the centromeric or subtelomeric regions in Triticeae species (Poaceae) and its evolution in wheat.

The TaiI family sequences are classified as tandem repetitive DNA sequences present in the genome of tribe Triticeae, and are localized in the centromeric regions of common wheat, but in the subtelomeric heterochromatic regions of Leymus racemosus and related species. In this study, we investigated the chromosomal distribution of TaiI family sequences in other Triticeae species. The results demonstrated a centromeric localization in genera Triticum and Aegilops and subtelomeric localization in other genera, thus showing a genus-dependent localization of TaiI family sequences in one or the other region. The copy numbers of TaiI family sequences in species in the same genus varied greatly, whether in the centromeric or subtelomeric regions (depending on genus). We also examined the evolution of TaiI family sequences during polyploidization of hexaploid common wheat. A comparison of chromosomal locations of the major TaiI family signals in common wheat and in its ancestral species suggested that the centromeric TaiI family sequences in common wheat were inherited from its ancestors with little modification, whereas a mixed origin for the B genome of common wheat was indicated.     

小麦根际联合固氮菌(固氮螺菌,Azospirillum brasilense)田间接种效果的研究

据黑龙江省1990年7个中试点试验证明,小麦根际联合固氮菌田间接种效果在5.2—20.6％,平均为9.8％;每田可增产小麦19.1公斤。小麦根际联合固氮菌能促进小麦本长发育,在生育期间可使株高、鲜重增加,叶色变缘。秋收考种证明,对产量构成因子的平方米穗数、穗粒数和千粒重均有增加。