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11.
Small ubiquitin-like modifier (SUMO), a member of the ubiquitin-related protein family, is covalently conjugated to lysine residues of its substrates in a process referred to as SUMOylation. SUMOylation occurs through a series of enzymatic reactions analogous to that of the ubiquitination pathway, resulting in modification of the biochemical and functional properties of substrates. To date, four mammalian SUMO isoforms, a single heterodimeric SUMO-activating E1 enzyme SAE1/SAE2, a single SUMO-conjugating E2 enzyme ubiquitin-conjugating enzyme E2I (UBC9), and a few subgroups of SUMO E3 ligases have been identified. Several SUMO E3 ligases such as topoisomerase I binding, arginine/serine-rich (TOPORS), TNF receptor-associated factor 7 (TRAF7), and tripartite motif containing 27 (TRIM27) have dual functions as ubiquitin E3 ligases. Here, we demonstrate that the ubiquitin E3 ligase UHRF2 also acts as a SUMO E3 ligase. UHRF2 effectively enhances zinc finger protein 131 (ZNF131) SUMOylation but does not enhance ZNF131 ubiquitination. In addition, the SUMO E3 activity of UHRF2 on ZNF131 depends on the presence of SET and RING finger-associated and nuclear localization signal-containing region domains, whereas the critical ubiquitin E3 activity RING domain is dispensable. Our findings suggest that UHRF2 has independent functional domains and regulatory mechanisms for these two distinct enzymatic activities.  相似文献   
12.
Changes in composition of both total aerobes and anaerobes of rat intestinal microflora do not appear to affect the metabolism of taurolithocholic acid.  相似文献   
13.
AnEscherichia coliexpression system that exploits the bacterial alkaline phosphatase (PhoA) signal sequence to translocate recombinant human epidermal growth factor (hEGF) to the periplasm was used to evaluate how changes in the composition and sequence of amino acids near the PhoA–hEGF junction influence the periplasmic accumulation of recombinant protein. A series of chimeric structural genes was generated byin vitroreplacement of hEGF sequence with analogous segments from the EGF-like domain of human heregulin (HRG), significantly altering the electrostatic character of the amino-terminal region of the mature protein. Quantitation of HRG/EGF protein inE. coliperiplasmic extracts, by RP-HPLC, showed a fourfold decrease after one of two acidic residues located in the amino-terminal region of the mature hEGF, near the PhoA junction, was replaced. An additional threefold decrease was observed when the second acidic residue was replaced with a positively charged lysine. Further extension of the amino-terminal HRG sequence, beyond the first six residues, resulted in net neutralization of a more distant EGF acidic residue with no additional effect on protein yield. The importance of having a negatively charged group in the amino-terminal region of the mature protein was confirmed when insertion of an aspartic acid near the amino-terminus of two poorly expressed hybrid protein sequences resulted in a five- to eightfold increase in their recovery from the periplasm. This study demonstrates the importance of having negatively charged residues near the fusion junction of recombinant proteins expressed inE. coliusing the PhoA signal sequence for protein export.  相似文献   
14.
15.
The c-myc gene encodes superimposed RNA polymerase II and III promoters   总被引:25,自引:0,他引:25  
J Chung  D J Sussman  R Zeller  P Leder 《Cell》1987,51(6):1001-1008
  相似文献   
16.
An external 3.8-MeV proton beam was employed to induce X-rays in 100-mg pellets of human follicular fluids and in 4–8 mg pellets of spermatozoa. The elements Cl, K, Ca, Fe, Cu, Zn, and Br were quantitatively determined in follicular fluids, whereas the elements, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, and Zn were determined in the spermatozoa. Both samples had high interelement Spearman correlation coefficients. Correlations of elements in the samples were observed with several clinical parameters. The multielemental analysis of spermatozoa can be used to approximate quantities of trace elements inserted into the egg ooplasm at the time of fertilization. These elemental quantities appear to be in the femtogram (10?15) range.  相似文献   
17.
A 6.8-kilobase-pair (kbp) transposable element (Tn4556) was found in a neomycin-producing strain of Streptomyces fradiae. This element was first observed in two 30.3-kbp plasmids (pUC1123 and pUC1124) which arose when a thiostrepton resistance gene (1 kbp) was ligated with the BclI-2 fragment (22.5 kbp) that contains the origin of replication of phage SF1. The Tn4556 segment was deleted when these plasmids were transduced into another S. fradiae host with phage SF1. These deletion plasmids (pUC1210 and pUC1211) had copy numbers of less than 1 per chromosome and were unstable. In contrast, pUC1123 and pUC1124, with copy numbers of 12 to 15 per chromosome, respectively, were relatively stable. When pUC1210 and pUC1211 were reintroduced into S. fradiae by protoplast transformation, the Tn4556 element transposed again to the plasmids at numerous new locations in either of two orientations. A copy of Tn4556 was found in the S. fradiae chromosome by hybridization studies. It appears that Tn4556 originated from the chromosome, transposed into unstable pUC1210 and pUC1211, and made stable plasmids. A temperature-sensitive hybrid plasmid carrying a viomycin resistance derivative of Tn4556 (pMT660::Tn4556::vph) was constructed. When Streptomyces lividans UC8390 containing the hybrid plasmid was grown at 39 degrees C, Tn4556::vph (Tn4560) transposed to random positions in the host chromosome.  相似文献   
18.
The PvuII fragment of human genomic clone LCV-517 which contains the entire coding region of a beta-adrenergic receptor gene was cloned into the SmaI site of the expression vector pMSG. The recombinant DNA was cotransfected with pRSVneo into mouse B-82 cells using the CaPO4 precipitation method. B-82 cells do not possess beta-adrenergic receptors but do contain prostaglandin E1 receptors that stimulate adenylate cyclase. Following transfection, several colonies expressing beta-adrenergic receptors were isolated. Analysis of ligand binding to expressed beta-receptors indicated that the protein encoded by the gene in clone LCV-517 was a beta 2-adrenergic subtype. Human beta 2-adrenergic receptors photoaffinity labeled with [125I]iodocyanopindolol diazirine migrated on sodium dodecyl sulfate-polyacrylamide gels consistent with a molecular mass of 68,000, demonstrating that the receptor is glycosylated to an extent of 25-30% by weight. Addition of isoproterenol to cultures of transfected cells resulted in a 3-4-fold stimulation of adenylate cyclase, an effect similar to that seen in control B-82 cells with prostaglandin E1. These data describe the production of stable murine clonal cell lines expressing human beta 2-adrenergic receptors and illustrate the utility of such lines in the biochemical and pharmacological characterization of receptor proteins.  相似文献   
19.
Stimulation of glutamate binding by the dipeptide L-phenylalanyl-L-glutamate (Phe-Glu) was inhibited by the peptidase inhibitor bestatin, suggesting that the stimulation was caused by glutamate liberated from the dipeptide and not by the dipeptide itself. It further suggests that this form of glutamate binding should be reinterpreted as glutamate sequestration and that stimulation of binding both by dipeptides and after preincubation with high concentrations of glutamate is likely to be due to counterflow accumulation. Several other criteria indicate that most of glutamate binding stimulated by chloride represents glutamate sequestration: Binding is reduced when the osmolarity of the incubation medium is increased, when membranes incubated with [3H]glutamate are lysed before filtration, and when membranes are made permeable by transient exposure to saponin. Moreover, dissociation of bound glutamate after a 100-fold dilution of the incubation medium is accelerated about 50 times by the addition of glutamate to the dilution medium. This result would be anomalous if glutamate were bound to a receptor site; it suggests instead that glutamate is transported in and out of membrane vesicles by a transport system that preferentially mediates exchange between internal and external glutamate. Glutamate binding contains a component of glutamate sequestration even when measured in the absence of chloride. Sequestration is adequately abolished only after treating membranes with detergents; even extensive lysis, sonication, and freezing/thawing may be insufficient.  相似文献   
20.
A cDNA library representing total poly(A+) RNA from the livers of male B10.WR mice was screened with a 1097 base pair (bp) probe obtained from a partial human C4b-binding protein (C4BP) cDNA clone. Two cDNA clones were isolated, the largest of which was sequenced and found to be 1889 bp in length exclusive of the poly(A) tail. The predicted mouse C4BP polypeptide chain encoded by 1239 bp is 413 amino acid residues in length and has a calculated molecular weight of 45,281. The 370-nucleotide sequence upstream from the codon for the predicted amino terminus contains two possible in-phase translational start signals which yield leader sequences of 56 and 13 amino acid residues, respectively. The 3'-untranslated region is 277 bp long, and there are two potential overlapping poly(A) recognition signals, AATTAA and ATTAAAA, located 26 and 25 bp, respectively, upstream from the poly(A) tail; these are preceded by five other potential polyadenylation signals. Beginning at the amino terminus and continuing through to residue 358, there are six contiguous regions of internal homology, each about 60 amino acids in length. The carboxy-terminal 55 amino acid sequence shares no homology with the repeating units. Extensive homology was found with human C4BP at the amino acid level (61%) as well as at the nucleotide level for both the coding and 3'-untranslated regions. Significant differences, however, were observed between mouse and human C4BP.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
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