Genetic selection for active E.coIi amber tRNAASn exclusively led to glutamine inserting suppressors

International audienceSuppressor tRNAs are useful tools for determining identity elements which define recognition of tRNAs in vivo by their cognate aminoacyl-tRNA synthetases. This study was aimed at the isolation of active amber tRNAASn. Nineteen mutated tRNAASnfcuA having amber suppressor activity were selected by an in vivo genetic screen, and all exclusively inserted glutamine. From analysis of the different mutations it is concluded that glutamine accepting activity was obtained upon reducing the interaction strength between the first base pair of the tRNAASnfCuA by direct or indirect effects. Failure to isolate tRNAASnfcuA suppressors charged with asparagine as well as other evolutionary related amino acids is discussed

Crosslinking of elongation factor Tu to tRNAPhe by trans-diamminedichloroplatinum (II) Characterization of two crosslinking sites on EF-Tu

AbstractIn a preceding paper [(1987) Nucleic Acids Res. 15, 5787–5801], we have used trans-diamminedichloroplatinum (II) to induce reversible RNA-protein crosslinks within the ternary EF-Tu/GTP/Phe-tRNAPhe complex and have identified two crosslinking sites on the tRNA. The aim of the present paper is to determine the crosslinking sites on EF-Tu. Two tryptic peptides located in domain I could be identified, a major one (residues 45–74) and a minor one (residues 117–154). The use of Staphylococcus aureus V8 protease led to the isolation of two major peptides (residues 56–68 and 64–68) and one minor peptide (118–124). These results are discussed in the light of the current knowledge of the topography of the EF-Tu/tRNA complex

Catalytic IgG from patients with hemophilia A inactivate therapeutic factor VIII

Factor VIII (FVIII) inhibitors are anti-FVIII IgG that arise in up to 50% of the patients with hemophilia A, upon therapeutic administration of exogenous FVIII. Factor VIII inhibitors neutralize the activity of the administered FVIII by sterically hindering its interaction with molecules of the coagulation cascade, or by forming immune complexes with FVIII and accelerating its clearance from the circulation. We have shown previously that a subset of anti-factor VIII IgG hydrolyzes FVIII. FVIII-hydrolyzing IgG are detected in over 50% of inhibitor-positive patients with severe hemophilia A, and are not found in inhibitornegative patients. Although human proficient catalytic Abs have been described in a number of inflammatory and autoimmune disorders, their pathological relevance remains elusive. We demonstrate here that the kinetics of FVIII degradation by FVIIIhydrolyzing IgG are compatible with a pathogenic role for IgG catalysts. We also report that FVIII-hydrolyzing IgG from each patient exhibit multiple cleavage sites on FVIII and that, while the specificity of cleavage varies from one patient to another, catalytic IgG preferentially hydrolyze peptide bonds containing basic amino acids

Functional characterization of the proteolytic activity of the tomatoblack ring nepovirus RNA-1-encoded polyprotein

AbstractTranslation of tomato black ring virus (TBRV) RNA-1 in a rabbit reticulocyte lysate leads to the synthesis of a 250Kpolyprotein which cleaves itself into smaller proteins of 50, 60, 120, and 190K. Polypeptides synthesized from synthetic transcripts corresponding to different regions of TBRV RNA-1 are processed only when they encode the 23K protein delimited earlier by sequence homology with the cowpea mosaic virus 24K protease. The proteolytic activity of this protein is completely lost by mutating residues C170 (to I) or L188 (to H), residues which align with conserved residues of the viral serine-like proteases. The 120K protein is generated by cleavage of the dipeptide K/A localized in front of the VPg but is not further cleaved in vitro at the K/S site (at the C terminus of the VPg) or between the protease and polymerase domains. However, both the protein VPgProPol (120K) and the protein ProPol (117K) produced in vitro from synthetic transcripts can cleave in trans the RNA-2-encoded 150K polyprotein, but they cannot cleave in trans polypeptides containing a cleavage site expressed from RNA-1 transcripts in which the protease cistron is absent or modified

IgG from patients with systemic sclerosis bind to DNA antitopoisomerase 1 in normal human fibroblasts extracts

Mathieu C Tamby1, Amélie Servettaz1, Nicolas Tamas1, Joseph Reinbolt2, Frédéric Caux3, Olivier Meyer4, Yannick Allanore5, André Kahan5, Loïc Guillevin6, Luc Mouthon1,61Paris-Descartes University, Faculty of Medicine, UPRES-EA 4058, Paris, France; 2UPR 9002, Centre National de la Recherche Scientifique, Strasbourg, France; 3UPRES EA 2436, Paris-Nord University, Bobigny, France; 4Rheumatology Department, Bichat Hospital, Assistance Publique-Hôpitaux de Paris (AP-HP), Paris, France; 5Rheumatology A Department, Cochin Hospital, AP-HP; 6Paris-Descartes University, Faculty of Medicine, Department of Internal Medicine and French Reference Center for Necrotizing Vasculitides and Systemic Sclerosis, Cochin Hospital, AP-HP, Paris, FranceAbstract: By using a semi-quantitative immunoblotting technique, we have analyzed serum immunoglobulin G (IgG) reactivities of patients with limited cutaneous systemic sclerosis and anticentromere antibodies, patients with diffuse systemic sclerosis and antitopoisomerase 1 antibodies, patients with diffuse systemic sclerosis without antitopoisomerase 1 or anticentromere antibodies and age- and gender-matched healthy controls with normal human skin fibroblasts and HEp-2 cells antigens. Serum IgG reactivities of patients with diffuse systemic sclerosis and antitopoisomerase 1 antibodies differed significantly from those of healthy controls or systemic sclerosis patients in other groups for reactivity with fibroblast proteins. IgG from patients with antitopoisomerase 1 antibodies bound to a 90 kDa fibroblast band and to a 100 kDa protein band in a HEp-2 cell protein extract. These two bands were further identified as DNA topoisomerase 1. Our results indicate that IgG from patients with diffuse systemic sclerosis bind DNA topoisomerase 1 in normal human fibroblasts extracts.Keywords: systemic sclerosis, autoantibodies, IgG, fibroblast, DNA topoisomerase