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D Schock

Publications and source records attributed to D Schock.

9 recordsLinked to original sources
PubMed1999

Tissue-specific differences in the role of RNA 3' of the apolipoprotein B mRNA mooring sequence in editosome assembly.

Site-specific editing of apolipoprotein B (apoB) mRNA by the cytidine deaminase, APOBEC-1 is proposed to require interactions of auxiliary protein(s) with an eleven nucleotide element, the mooring sequence, located 3' of the C --> U editing site. An analysis of the RNA sequence dependence for protein-RNA interactions and editosome assembly in rat liver and the small intestine demonstrated that the mooring sequence was a minimal requirement for these interactions. Sequences 3' of the mooring sequence either interacted with 66 kDa and 44 kDa proteins or enhanced the interactions of these proteins with the mooring sequence. The data also suggested tissue-specific differences in the relative importance of the 3' cis-acting 'enhancer' elements in the efficiency or stability of editosome assembly. We propose that the previously demonstrated differences in apoB mRNA editing efficiency and its regulation in liver and intestine may in part be due to differences in auxiliary protein interactions with apoB mRNA 3' of the mooring sequence.

Animals↗
PubMed1999

Pathology, isolation, and preliminary molecular characterization of a novel iridovirus from tiger salamanders in Saskatchewan.

All iridovirus was confirmed to be the cause of an epizootic in larval and adult tiger salamanders (Ambystoma tigrinum diaboli) from four separate ponds in southern Saskatchewan (Canada) during the summer of 1997. This organism also is suspected, based on electron microscopic findings, to be the cause of mortality of larval tiger salamanders in a pond over 200 km to the north during the same year. Salamanders developed a generalized viremia which resulted in various lesions including: necrotizing, vesicular and ulcerative dermatitis; gastrointestinal ulceration; and necrosis of hepatic, splenic, renal, lymphoid, and hematopoietic tissues. In cells associated with these lesions, large lightly basophilic cytoplasmic inclusions and vacuolated nuclei with marginated chromatin were consistently found. Virus was isolated from tissue homogenates of infected salamanders following inoculation of epithelioma papilloma cyprini (EPC) cells. The virus, provisionally designated Regina ranavirus (RRV), was initially identified as an iridovirus by electron microscopy. Subsequent molecular characterization, including partial sequence analysis of the major capsid protein (MCP) gene, confirmed this assignment and established that RRV was a ranavirus distinct from frog virus 3 (FV3) and other members of the genus Ranavirus. Intraperitoneal inoculation of 5 x 10(6.23) TCID50 of the field isolate caused mortality in inoculated salamanders at 13 days post infection. Field, clinical, and molecular studies jointly suggest that the etiological agent of recent salamander mortalities is a highly infectious novel ranavirus.

Ambystoma↗
PubMed1996

An auxiliary factor containing a 240-kDa protein complex is involved in apolipoprotein B RNA editing.

A protein complex involved in apolipoprotein B (apoB) RNA editing, referred to as AUX240 (auxiliary factor containing p240), has been identified through the production of monoclonal antibodies against in vitro assembled 27S editosomes. The 240-kDa protein antigen of AUX240 colocalized with editosome complexes on immunoblots of native gels. Immunoadsorbed extracts were impaired in their ability to assemble editosomes beyond early intermediates and in their ability to edit apoB RNA efficiently. Supplementation of adsorbed extract with AUX240 restored both editosome assembly and editing activities. Several proteins, in addition to p240, ranging in molecular mass from 150 to 45 kDa coimmunopurify as AUX240 under stringent wash conditions. The activity of the catalytic subunit of the editosome APOBEC-1 and mooring sequence RNA binding proteins of 66 and 44 kDa could not be demonstrated in AUX240. The data suggest that p240 and associated proteins constitute an auxiliary factor required for efficient apoB RNA editing. We propose that the role of AUX240 may be regulatory and involve mediation or stabilization of interactions between APOBEC-1 subunits and editing site recognition proteins leading the assembly of the rat liver C/U editosome.

Animals↗
PubMed1994

Only cytidines 5' of the apolipoprotein B mRNA mooring sequence are edited.

A 22 nucleotide 'cassette' containing three distinct sequence elements is required for efficient apolipoprotein B (apoB) RNA editing. One of the elements, the mooring sequence, has been proposed as the apoB RNA-recognition element in binding 66 and 44 kDa proteins during editosome assembly. We show here that editing can only take place on cytidines 5' of the mooring sequence; thereby providing further proof for the proposed orientation-specific assembly of editing factors at the editing site. We also provide direct evidence for the existence of a cryptic mooring sequence immediately downstream of the wild-type editing site (between nucleotides 6688-6710). When a cytidine is introduced 5' of this site (at nucleotide 6687), editing occurs at wild-type (nucleotide 6666) and cryptic sites. The cytidine to be edited is not involved in 66 and 44 kDa protein binding, and therefore, the data suggest that the cryptic mooring sequence binds these factors, and may facilitate factor recruitment to the wild-type editing site. These data may also explain why wild-type levels of editing on chimeric, RNA editing substrates can only be achieved when the 22 nucleotide editing cassette is flanked 3' by apoB RNA sequence.

Apolipoproteins B↗
PubMed1976

TRH-degrading enzyme activity in peripheral and pituitary-portal plasma of the rat.

The enzymatic degradation of TRH was measured in peripheral and pituitary-portal plasma. Enzyme activity in peripheral plasma was 3.20 pg/min/mug plasma protein; in pituitary-portal plasma the rate of degradation was only 0.83 pg/min/mug protein. After dialysis, which removed virtually all endogenous TRH and LHRH, enzyme activity in peripheral and portal plasma was 2.24 and 0.60 pg/min/mug respectively. These data suggest that portal plasma contains large concentrations of unidentified substances which are competitive inhibitors or substrates for the enzyme or that portal plasma contains less TRH-degrading enzyme.

Animals↗
PubMed1975

Characteristics of the plasma TRH-degrading enzyme.

The reaction products of plasma enzyme degradation of TRH were identified by thin layer chromatography. The enzyme in normal rat plasma yields proline and pGlu-His as major reaction products. High concentrations of proline decrease peptide cleavage, resulting in greater amounts of acid TRH. The apparent Km of the enzyme is 4.1 X 10(-6) M. LHRH and neurotensin are competitive inhibitors with Ki of 5 X 10(-6) M and 1.5 X 10(-5) M, respectively. Somatostatin, MIF, oxytocin, arg-vasopressin, arg-vasotocin, neurophysin II and glucagon do not compete; and pGlu-His-Pro-OH, Glu-His-Pro-OH, pGlu-His, His-Pro-NH2, and Pro-NH2 do not affect enzyme activity. These data suggest that the substrated requires pGlu and a terminal or internal amide to complex with the enzyme. The enzyme is markedly inhibited by Cu++, Bal, benzamadine, p-(chloromercuri)-benzoic acid, moderately affected by EDTA and puromycin, and unaffected by mercaptoethanol. TSH does not affect enzyme activity while LH inhibits it moderately at high concentrations (300-600 pg/ml).

Animals↗