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Biomedical subjects

T Twardowski

Publications and source records attributed to T Twardowski.

At least 37 records · Page 2Linked to original sources
PubMed1987

Platelet glycoprotein concentrations in patients with chronic uraemia.

In 15 patients with chronic uraemia and 9 healthy subjects concentrations of platelets glycoproteins Ib, IIb, and IIIa were determined. There were no differences between patients and control group. The possible role of glycoproteins in disturbances of the platelets function is discussed.

Adult↗
PubMed1984

Two initiation sites detected in the small s1 species of reovirus mRNA by dipeptide synthesis in vitro.

Reovirus mRNAs directed the synthesis of fMet dipeptides in a translation initiation system reconstituted from rabbit reticulocyte initiation and elongation factors, Artemia salina 80S ribosomes, yeast fMet-tRNAiMet and Escherichia coli3H-labeled aminoacyl tRNAs. As predicted from the GC(U,G) codon that follows the 5'-proximal AUG in half of the viral mRNA species, fMet-Ala was the predominant dipeptide product obtained in response to a mixture of mRNAs or to the separated size classes of medium (m) and small (s) mRNA. The four individual small mRNA species each directed the synthesis of an fMet dipeptide that was consistent with the utilization of the 5'-proximal AUG for initiation. In addition to fMet-Asp, the s1 mRNA also directed fMet-Glu synthesis indicative of initiation in a second reading frame at the 5'-penultimate AUG. The tripeptide fMet-Glu-Tyr was also synthesized from s1 mRNA, which further verified this second initiation site. mRNAs containing 5'-terminal GpppG were 10-15% as active as the corresponding m7G-capped templates. The dipeptide assay provides a rapid method for determining initiation sites in individual mRNAs or in mixtures of mRNAs.

Amino Acid Sequence↗
PubMed1983

Identification of uracil as a major lesion in E. coli DNA following the incorporation of 5-bromouracil, and some of the accompanying effects.

Cultivation of E. coli cells in the presence of 5-bromodeoxyuridine (BUdR) leads to formation of lesions in the cellular DNA which affect its secondary structure, as reflected by changes in temperature profiles. Such DNA contains single-stranded regions susceptible to endonuclease S1. One of the major sources of the BU-induced lesions appears to be dehalogenation of incorporated 5-bromouracil (BU) residues, with accompanying formation of uracil. The presence of uracil residues in such DNA was demonstrated directly by chromatography of hydrolyzates, and by the susceptibility of such residues to uracil-DNA glycosylase. The number of uracil residues was dependent on the extent of damage in the DNA, and decreased during the DNA repair that accompanied reactivation of bromouracil-inactivated cells. Dehalogenation of incorporated BU presumably results in formation of apyrimidinic sites by uracil-DNA glycosylase, and then single-strand nicks either by AP-endonuclease and/or dehalogenation. The findings are relevant to the mechanism of BU-induced mutagenesis.

Bromodeoxyuridine↗
PubMed1983

Simplified in vitro system for study of eukaryotic mRNA translation by measuring di- and tripeptide formation.

An in vitro system for measurement of rabbit globin mRNA translation has been developed based on the formation of the NH2-terminal dipeptide, fMet-Val. The basic components include a partially purified initiation factor preparation from rabbit reticulocytes supplemented with eukaryotic initiation factor 4A, purified and formylated yeast Met-tRNAi, and rabbit liver or Escherichia coli Val-tRNA1Val. Picomole quantities of fMet-Val are synthesized, dependent on mRNA, and the dipeptide is readily assayed by a simple extraction procedure. In the presence of Leu-tRNA or His-tRNA, the tripeptides fMet-Val-Leu and fMet-Val-His are synthesized, corresponding to the NH2-terminal sequence of alpha- and beta-globin, respectively. Therefore, tripeptide synthesis provides a simple means to distinguish between the expression of the alpha- and beta-globin mRNA species.

Animals↗
PubMed1982

The elongation factor 1 from wheat germ: structural and functional properties.

Three forms of elongation factor 1 (EF1A, EF1B and EF1C) were isolated from wheat germ; the preparation obtained by successive chromatography on DEAE-Sephadex A-50, hydroxylapatite and Sephadex G-200 showed about 90% purity. The molecular masses of these forms were about: 61 000, 48 000 and 12 500, respectively. EF1A was the only form which formed the ternary complex GTP-EF1-AA-tRNA and was the most active in binding of Phe-tRNA to the poly-U programmed ribosomes. Based on the data of amino acid analysis, N-terminal amino acid determination and previously described proteolysis (Pulikowska et al., Biochem. Biophys. Res. Commun., 1979, 91, 1011-1017), it is assumed that EF1C is a basic structural subunit of elongation factor EF1 from wheat germ, but only EF1A shows the conformation-dependent full biological activity.

Amino Acids↗
PubMed1978

Binding of reticulocyte elongation factor 1 to ribosomes and nucleic acids.

The present study has examined the requirements for the binding of rabbit reticulocyte elongation factor 1 (EF-1) to ribosomes under different assay conditions. When a centrifugation procedure was used to separate the ribosome EF-1 complex, the binding of EF-1 to ribosomes required GTP and Phe-tRNA, but not poly(U). The results suggested that undr these conditions a ternary complex, EF-1 . GTP . aminoacyl-tRNA, is necessary for the formation of a ribosome . EF-1 complex. However, when gel filtration was used to isolate the ribosome . EF-1 complex, only template and tRNA were required. These studie emphasize the fact that the procedure used to isolate the ribosome . EF-1 complex determines the requirements for stable complex formation. EF-1 can also interact with nucleic acids such as 28 S and 18 S rRNA, messenger RNA and DNA. In contrast to the binding to ribosomes, EF-1 binding to nucleic acids requires only Mg2+.

Animals↗
PubMed1977

Interaction of elongation factor 2 from wheat germ with guanosine nucleotides and ribosomes.

1. The amino acid composition of wheat germ EF2 differs to some extent from that of elongation factors from mammals and bacteria. 2. The purified wheat germ EF2, similarly as the factors from other sources, is active in the: EF1-dependent polymerization of phenylalanine; ribosome-dependent GTP hydrolysis; binding of guanosine nucleotides; and ADP-ribosylation in the presence of diphtheria toxin. Fusidic acid at a concentration of 1 mM inhibits all these EF2-dependent reactions. 3. Diphtheria toxin in the presence of NAD+ inhibits polymerization of phenylalanine but does not effect GTP binding to EF2. 4. Binding of GDP to wheat germ EF2 is inhibited by ribosomes. During interaction with ribosomes, GTP in EF2-GTP complex is rapidly hydrolysed to GDP. Both GTP and 5'-guanylmethylenediphosphonate competitively inhibit formation of the ribosome-EF2-GDP complex due to the replacement of GDP from the complex. The latter is stabilized by fusidic acid.

Adenosine Diphosphate↗