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The monomeric haemoglobin IV from Chironomus thummi thummi (CTT IV) is an allosteric protein characterized by pH-dependent ligand affinities (Bohr-effect). The ligand-linked proton dissociation gives rise to a t r conformational transition. Furthermore, the Bohr-effect is ligand-dependent and decreases in magnitude following the order of ligands, O2 > CO > NO. Although the Bohr-effect for NO is smallest, the electron spin resonance (ESR) spectra of frozen solutions of 15NO-ligated CTT IV measured as higher derivatives at 77 K reflect this pH-dependent conformation change. g Tensor and hyperfine constants coinciding with the principal directions of the g tensor have been evaluated for 57Fe, 15NO, 14NE-imidazole, and 14N-pyrroles.Hyperfine parameters and g values of both conformation states of this haemoglobin, i.e., of the t state at low pH with low ligand affinity and of the r state at high pH with high ligand affinity, are characteristic for a hexacoordinated nitrosyl haem complex. The change in pH leads to a variation of the Fe-N-O bond angle which is larger at high pH (r conformation) than at low pH (t conformation). Furthermore, the spin transfer from NO into iron orbitals is larger at high pH than at low pH. These results are consistent with the assumption that the interaction of proximal imidazole and iron is smaller in the r conformation than in the t conformation.Binding of anionic detergents to nitrosyl CTT IV causes a conversion of the native (t, r) into a denatured (super-r) structure. The latter, on the basis of hyperfine and g values, apparently contains a pentacoordinated nitrosyl haem complex. Because of the extreme displacement of the proximal imidazole in the super-r structure, the Fe-N-O gouping is nearly linear and a large spin transfer from NO into iron orbitals occurs. Removal of anionic detergents from the protein leads to a full reconversion of the super-r into the native conformations.These structure-related changes of hyperfine constants and g tensor further support the assumption that the trans-effect of the proximal imidazole is an important link of allosteric interactions in haemoglobins.  相似文献   

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A DNA fraction has been isolated from total Chironomus thummi thummi DNA which is discernible from the bulk Ch. th. thummi DNA by a lower thermal stability. In situ hybridizations with polytene salivary gland chromosomes of Ch. th. thummi and Ch. th. piger made localization of this DNA fraction possible. Hybridizations with bands which contain different amounts of DNA in the two subspecies indicate that the isolated DNA fraction mostly consists of those sequences which represent the genetical difference between thummi and piger.This paper is dedicated to Professor Dr. H. Bauer on the occasion of his 75th birthday  相似文献   

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Summary A 1.7 kb long transposable element called TECth1 was found in the 3 flanking region of aChironomus thummi Balbiani ring gene. As shown by sequence comparison with a second copy, TECthl is characterized by a perfect terminal inverted repeat of 17 by flanked by a duplicated target site of 8 bp, four internal imperfect inverted repeats of 17 to 26 by and terminal regions of about 0.25 kb with a high number of short direct repeats of the consensus sequence ACTTT or permutated and mutated forms such as TTTAC or ACTAT. The terminal inverted repeats and the 8 by target site duplication are reminiscent ofDrosophila P and hobo elements but no long open reading frame starting with ATG is present, suggesting that the two TECthl copies studied represent deletion derivatives of a longer element coding for its own transposase. In situ hybridization revealed about 75 labelled sites distributed over all chromosomes with the Balbiani ring locus most strongly labelled. Fifty percent of the sites are specific for a given individual, and these variable sites are often heterozygous for the element.  相似文献   

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The repetition frequency of a highly repetitive DNA sequence has been measured in the genomes of Ch. thummi thummi and Ch. th. piger. This sequence is known to be involved in the evolutionary duplication of defined chromosomal segments leading to a significant increase in the genome size of Ch. th. thummi. Reassociation of this highly repetitive DNA sequence which has a repeat length of 120 base-pairs, with total Ch. th. thummi and Ch. th. piger DNA has shown that the repetition frequency in the Ch. th. thummi DNA is 5.5 fold higher than in Ch. th. piger. In both genomes a 120 base-pair sequence is present as tandemly repeated sequence as shown by Southern analysis.  相似文献   

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The formation of a new telomeric Balbiani ring in the right arm of chromosome III (T-BR III) has been induced in Chironomus thummi larvae by applying a wide range of temperature treatments (33 °–39 ° C). In this paper we present some kinetic and functional characteristics of this structure. T-BR III incorporates tritiated uridine, and during its formation accumulation of acidic proteins takes place. However, induction and maintenance of this puff structure appear to be insensitive to Actinomycin treatment. An additional T-BR can be induced in chromosome I by employing the most drastic temperature treatments (37 °–39 ° C). We also report the existence of a group of puffs active after heat treatments in Chironomus polytene chromosomes which could be homologous with the T-puffs of Drosophila.  相似文献   

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The ribosomal DNAs from Ch. thummi piger and Ch. th. thummi were cloned and analysed by a variety of restriction endonucleases. Comparison of rDNA clones from the two subspecies revealed a considerable length difference: the length of the analysed rDNA cistrons is approximately 9.0 kb for Ch. th. piger and approximately 14.5 kb for Ch. th. thummi. The nearly 5 kb additional DNA in Ch. th. thummi is clearly located within the non-transcribed spacer region, and consists of AT-rich, reptitive DNA elements. These elements with a basic repeat length of approximately 120 bp, are arranged tandemly in stretches of up to about 50 identical copies, which are characterized by a cleavage site for ClaI restriction endonuclease. They are found only in the Ch. th. thummi rDNA clones and not in the Ch. th. piger clones. Southern hybridizations between cloned ribosomal DNA and centromeric highly repetitive DNA have shown that the ribosomal repetitive Cla-elements are closely related to a highly repetitive DNA sequence family, which is present in various chromosomal sites particularly the centromeres. Sequence analysis has revealed more than 90% homology between the ribosomal Cla-elements and the centromeric Cla-elements. — Since it is clear from cytological investigations that Ch. th. piger with the small rDNA repeating unit is the phylogenetically older subspecies, we postulate a transposition of Cla-elements into the nucleolar DNA during the evolution of Ch. th. thummi.  相似文献   

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Specific modification of the monomeric fraction III of ferri-hemoglobin from insect larvae Chironomus thummi thummi (Hb CTT) was studied on histidyl residues His-G19 (pK 4,8), His-E5 (pK 7,3) and Met-H22 at different pH using iodacetamide and spin label 2,2,6,6-tetramethyl-4-bromacethyl-piperidin-1-oxyl, an analogue of bromacetate. The analysis of the products of carboxymethylation (CM) showed that at pH 5,0 two products of modification CM-(His-G19)-Hb CTT, and CM-(Met-H22)-Hb CTT were obtained. In the case of modification at pH 7,2 with a spin label dicarboxymethylatid product CM-(His-G19)-CM (His-E5)-Hb CTT is obtained. In all products the degree of modification was one spin label per mole protein. Based on the data on the primery and tertiary structures Hb CTT and the results of the investigation, different reactivity of His-G19 and His-E5, as well as the cause of the absence of the product of carboxymethylation on His-G2 have been discussed. By analizing the absorption spectra of carboxymethylated derivatives of hemoglobin in the ultraviolet and visible region, as well as from the pH dependence curves of the absorption at Soret band in the interval pH 5,5-11,5 it has been shown that carboxymethylation of His-G19 and His E5 is not accompanied by any substantial disturbance of the structures of aquous-complexes Hb CTT. Modification of Met-H22 leads to strong changes in the absorption spectrum and to the absence of pH dependence of the absorption at Soret band, which indicates a change in the aquous-complexes Hb CTT structure.  相似文献   

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The dimeric haemoglobin CTT VIIB (Erythrocruorin) of Chironomus thummi thummi, Diptera, has been sequenced. Either globin or globin with maleic acid blocked lysines were cleaved with trypsin. The separation of peptides and the sequence analysis are given in detail.  相似文献   

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