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  • 1
    Electronic Resource
    Electronic Resource
    Circular ribosomal DNA and ribosomal DNA: replication in somatic amphibian cells (1975)
    Springer
    Chromosoma 52 (1975), S. 317-327 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Pulse labelled rDNA from cultured somatic cells of Xenopus laevis was examined by electron microscope autoradiography. The pattern of replication closely resembles that of bulk chromosomal DNA and differs considerably from rDNA synthesis during amplification in the oocyte. — About 0.15% of the rDNA molecules in the purified preparations were circular. The presence of interlocked circles of equal size indicates that the circles are not in vitro cyclization artefacts, but may represent free rRNA genes. A low frequency of circles was also seen in Xenopus blood rDNA. Their stability in high concentration of formamide suggests that they too did not arise after DNA extraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00364016
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  • 2
    Electronic Resource
    Electronic Resource
    A timing study of DNA amplification in Xenopus laevis oocytes (1971)
    Springer
    Chromosoma 35 (1971), S. 300-309 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The time course of meiotic amplification of nucleolar DNA in Xenopus laevis oocytes has been studied autoradiographically. We find that the process is first detectable in zygotene nuclei less than 7 days after the end of premeiotic S-phase. It is completed 3 1/2 weeks later, towards the end of pachytene. Premeiotic S-phase lasts for 1–2 weeks. We are not certain whether it is followed by a short G2 or whether leptotene commences immediately. Leptotene lasts for 5±2 days, zygotene for 7±2 days and pachytene for about 20 days before the oocyte gradually enters the extended diplotene stage. Various molecular mechanisms for amplification are discussed in the light of a 24±3 day amplification time. All are found to be potentially capable of amplifying sufficient nucleolar DNA in the time available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326280
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  • 3
    Electronic Resource
    Electronic Resource
    Limited polymorphism in HLA-DM does not involve the peptide binding groove (1994)
    Springer
    Immunogenetics 39 (1994), S. 56-58 
    Details
    ISSN: 1432-1211
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171797
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  • 4
    Electronic Resource
    Electronic Resource
    Alleles and haplotypes of the MHC-encoded ABC transporters TAP1 and TAP2 (1993)
    Springer
    Immunogenetics 37 (1993), S. 480-480 
    Details
    ISSN: 1432-1211
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00222478
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  • 5
    Electronic Resource
    Electronic Resource
    Zirconium-bearing aegirines from Motzfeldt, South Greenland (1981)
    Springer
    Contributions to mineralogy and petrology 75 (1981), S. 251-255 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Aegirines with almost 7.0 wt.% ZrO2 have been discovered in nepheline syenites from the Motzfeldt Centre, South Greenland. The analyses require the postulate of a new endmember pyroxene composition with the formula NaFM0.5Zr0.5Si2O6. A possible acronym is FM-NAZ. Aegirines rich in this component occur in rocks in which there is no other zirconium-bearing phase such as eudialyte. These zirconian pyroxenes have crystallised from magmas which were peralkaline, low in lime and silica and relatively low in oxygen fugacity compared with other nepheline syenites. These factors have combined to prevent the usual crystallisation of such Zr-phases as eudialyte, zircon or baddeleyite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01166764
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  • 6
    Electronic Resource
    Electronic Resource
    Light microscope autoradiography of ribosomal DNA amplification in Xenopus laevis (1974)
    Springer
    Chromosoma 46 (1974), S. 421-433 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A technique for the isolation of very high molecular weight rDNA1 from the ovary of Xenopus laevis is described. Tritiated rDNA was prepared by this method from ovaries at the amplification stage, and spread on slides for light microscope autoradiography. The average molecular weight of the spread DNA was greater than 180×106 daltons. Unlike chromosomal DNA grain tracks, rDNA tracks after 2 or 4 hours of labelling were not tandemly arranged. By allowing ovaries to equilibrate gradually with exogenous precursors, tracks showing a single gradient of grain density were produced, indicating that replication was proceeding in one direction at these sites. Bidirectional initiations, if they occur at all during amplification, are rare. The rate of rDNA chain growth is 10.5 μ/hour at 23° C, which is the same as the rate for chromosomal DNA synthesis in X. laevis. After 24 hours some tracks are over 200 μ long, suggesting that replication at a site may be continuous for at least this period. Although they do not distinguish between several alternative mechanisms, the results are compatible with a rolling circle mechanism for gene amplification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331630
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  • 7
    Electronic Resource
    Electronic Resource
    Alleles and haplotypes of the MHC-encoded ABC transporters TAP1 and TAP2 (1993)
    Springer
    Immunogenetics 37 (1993), S. 373-380 
    Details
    ISSN: 1432-1211
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract TAP1 and TAP2 are two major histocompatibility complex (MHC) genes, located between HLA-DP and -DQ, whose products form a transporter molecule involved in endogenous antigen processing. Polymorphic residues have been described in both genes and, in this study, we have identified another polymorphic site within the adenosine triphosphate (ATP)-binding domain of TAP2. We have used the amplification refractoru mutation system (ARMS) polymerase chain reaction (PCR) to characterize TAP1 and TAP2 alleles and haplotypes in a reference panel of 115 homozygous typing cell lines. Of four possible TAP1 alleles, we observed three, and of eight possible TAP2 alleles, we observed five. Among 88 (homozygous typing cells) (HTCs) homozygous at HLA-DR, -DQ and TP, 80 were also homozygous at TAP1 and TAP2. Of 27 HTCs homozygous at HLA-DR and -DQ, but heterozygous at -DP, 14 were homozygous at TAP1 or TAP2 and 13 heterozygous, consistent with recombination taking place either side of the TAP loci. Of the fifteen possible combinations of TAP1 and TAP2 alleles, we observed eleven, each at a frequency similar to that predicted by individual allele frequencies. In this ethnically heterogeneous panel there is no indication that particular combinations of TAP1 and TAP2 have been maintained together.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00216802
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  • 8
    Electronic Resource
    Electronic Resource
    Nerve growth factor. A structural relationship between its proteolytic and leukocyte-chemotactic active sites (1985)
    Springer
    Molecular and cellular biochemistry 66 (1985), S. 65-69 
    Details
    ISSN: 1573-4919
    Keywords: inflammation ; wound healing ; serine proteases ; chemotaxis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary High molecular weight mouse nerve growth factor(H M W-NGF), in addition to its effects on certain neural elements, is also chemotactic for human polymorphonuclear leukocytes. One of the subunits of H M W-NGF is a protease of the serine family and its active site contains a serine residue and a closely-neighboring histidine residue that are both essential for proteolysis. Elimination of enzyme activity by irreversibly blocking the single serine has no effect on leukotaxis, but blocking the histidine abolishes leukotaxis. These results suggest the possibility that part of the proteolytic active site of this enzyme may have evolved to perform more than one, completely different, biologic function — proteolysis as well as nonproteolytically mediated chemotaxis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231825
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  • 9
    Electronic Resource
    Electronic Resource
    Identification of a cDNA that encodes a 1-acyl-sn-glycerol-3-phosphate acyltransferase from Limnanthes douglasii (1995)
    Springer
    Plant molecular biology 29 (1995), S. 267-278 
    Details
    ISSN: 1573-5028
    Keywords: 1-acyl-sn-glycerol-3-phosphate acyltransferase ; complementation cloning ; Limnanthes douglasii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two different techniques were used to isolate potential cDNAs for acyl-CoA: 1-acyl-sn-glycerol-3-phosphate acyltransferase (LPA-AT) enzymes from Limnanthes douglasii. Both heterologous screening with the maize pMAT1 clone and in vivo complementation of the Escherchia coli mutant JC201 which is deficient in LPA-AT activity, were carried out. Clones identified by these procedures were different. Homology searches demonstrated that the clone isolated by heterologous probing, pLAT1, encodes a protein which is most similar to the maize (open reading frame in pMAT1) and yeast SLC1 proteins, which are putative LPA-AT sequences. This L. douglasii sequence shows much lower homology to the E. coli LPA-AT protein PlsC, which is the only LPA-AT sequence confirmed by over-expression studies. The clone isolated by complementation, pLAT2, encodes a protein with homology to both SLC1 and PlsC. It was not possible to over-express the complementing protein encoded by pLAT2 but further experimentation on membranes from complemented JC201 demonstrated that they possess a substrate specificity distinctly different from PlsC and similar to Limnanthes sp. microsome specificity. This data strongly supports the contention that pLAT2 is an LPA-AT clone. Northern blot analysis revealed different expression patterns for the two genes in pLAT1 and pLAT2. Transcription of the gene encoding the insert of pLAT2 occurred almost exclusively in developing seed tissue, whilst the cDNA of pLAT1 hybridised to poly(A)+ mRNA from seed, stem and leaf, demonstrating more widespread expression throughout the plant. Southern blot analysis indicated that the cDNA of pLAT2 was transcribed from a single-copy gene while that for pLAT1 was a member of a small gene family.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00043651
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  • 10
    Electronic Resource
    Electronic Resource
    Isolation and characterisation of a maize cDNA that complements a 1-acyl sn-glycerol-3-phosphate acyltransferase mutant of Escherichia coli and encodes a protein which has similarities to other acyltransferases (1994)
    Springer
    Plant molecular biology 26 (1994), S. 211-223 
    Details
    ISSN: 1573-5028
    Keywords: maize ; 1-acyl-sn-glycerol-3-phosphate acyltransferase ; complementation cloning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We selected cDNA plasmid clones that corrected the temperature-sensitive phenotype of Escherichia coli strain JC201, which is deficient in 1-acyl-sn-glycerol-3-phosphate acyltransferase activity. A plasmid-based maize endosperm cDNA library was used for complementation and a plasmid that enabled the cells to grow at 44°C on ampicillin was isolated. Addition of this plasmid (pMAT1) to JC201 restored 1-acyl-sn-glycerol-3-phosphate acyltransferase activity to the cells. Total phospholipid labelling showed that the substrate for the enzyme, lysophosphatidic acid, accumulated in JC201 and was further metabolised to phosphatidylethanolamine in complemented cells. Membranes isolated from such cells were able to convert lysophosphatidic acid to phosphatidic acid in acyltransferase assays. The cDNA insert of pMAT1 contains one long open reading frame of 374 amino acids which encodes a protein of relative molecular weight 42 543. The sequence of this protein is most similar to SLC1, which is thought to be able to acylate glycerol at the sn-2 position during synthesis of inositol-containing lipids. Homologies between the SLC1 protein, the 1-acyl-sn-glycerol-3-phosphate acyltransferase of E. coli (PlsC) and the maize ORF were found with blocks of conserved amino acids, whose spacing was conserved between the three proteins, identifiable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00039533
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