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Biomedical subjects

T Hultin

Publications and source records attributed to T Hultin.

At least 37 records · Page 2Linked to original sources
PubMed1979

Disulfide interaction in situ between two neighbouring proteins in mammalian 60-S ribosomal subunits. Isolation of the contact region of the larger protein.

A disulfide complex is formed in situ under gentle conditions between two neighbouring proteins in the 60-S subunits of mammalian ribosomes. The proteins have been identified as L 4 and L 29. The complex is easily isolated from whole ribosomes, and can be utilized for preparing the two proteins in a very pure state for further characterization. Chymotryptic cleavage of the complex or the isolated larger protein (L 4) in the presence of SDS produces two unequal fragments of this protein in nearly quantitative yield. The smaller fragment (approx. 12 000 daltons) contains the contact sequence. Only this fragment of protein L 4 is labelled when rat liver ribosomes are incuabted with iodo[14C]acetate under conditions of complex formation. Protein L 29 is resistant to chymotrypsin in the presence of sodium dodecyl sulfate.

Animals↗
PubMed1979

Early effects of dimethylnitrosamine on protein chain initiation and postmicrosomal polyadenylic acid-containing RNA content in mouse liver.

A mouse liver S-30 system was used to study the early effects of dimethylnitrosamine (DMNA) on polypeptide chain initiation and messenger RNA content. The inhibition of protein synthesis after DMNA administration was associated with a reduced capacity of the S-30 system to form 80S ribosomal initiation complexes. The binding of formylatable methionyl transfer RNA to polysomes was also depressed. The initiation defect was detectable in the assay system slightly later than the decrease in protein synthesis. Addition of mRNA stimulated both translation and 80S initiation complex formation but could not fully restore the activity of the S-30 system from DMNA-treated mice. A loss of poly(A)+ RNA from the postmicrosomal subfraction of the S-30 fraction was observed as early as 15 min after DMNA administration. Later, polyriboadenylic acid also decreased in the microsomal fraction. Monosomes accumulating in response to DMNA treatment were deficient in mRNA as measured by polyriboadenylic acid analysis. Conversely, the proportion of polyriboadenylic acid in the remaining polysomes increased, indicating that the mRNA had become less densely occupied with ribosomes.

Animals↗
PubMed1978

Stimulation of enzymatic phe-tRNA binding to mammalian ribosomes by thallium ions at concentrations blocking other ribosomal functions.

Thallium acetate (TIOAc) effectively stimulates poly(U)-directed Phe-tRNA binding to mouse ascitic tumour ribosomes under conditions when other ribosomal functions are completely blocked. The TI+ optimum is about 200 mM. The reaction is stimulated by EF-1, but not significantly by GTP. EF-1-dependent ribosomal GTPase is inhibited by T1+. The isolated Phe-tRNA . ribosome complex is relatively stable. The bound Phe-tRNA does not react with puromycin in the presence of 175 mM KCl. The complex formed in the presence of 90-100 mM TlOAc can, after isolation, be directly utilized for polyphenylalanine synthesis. The complex formed at 200 mM TlOAc is less active, apparently because of damage to the 60-S subunits. TlOAc at low concentrations (8 mM) stimulates K+ -containing poly(U)-translating systems, probably by stabilizing the translation complex.

Animals↗
PubMed1978

Preparation of projection-less particles from influenza virus and their messenger activities in prokaryotic and eukaryotic systems.

A fraction of projection-less particles was prepared from influenza A/Dunedin/4/73 and A/Victoria/3/75 (X-47) (H3N2) by detergent treatment and extraction into ether at 0 degrees C. The activity of this material in stimulating protein synthesis in vitro was studied and compared with that of isolated virion RNA using a) an RNA-dependent E. coli system, and b) a wheat germ system. In the bacterial system the purified RNA had the highest template activity, while in the eukaryotic system the disrupted particle preparation was by far the most active. Translation products were formed with immunological and electrophoretic properties similar to those of several influenza virion proteins. The experiments indicate that, when added in the form of disrupted projection-less particles, RNA from influenza A2 virus is utilized as a template by eukaryotic ribosomes.

Cell-Free System↗
PubMed1978

Activity of partially purified protein chain initiation factors from the livers of dimethylnitrosamine-treated rats.

Partially purified polypeptide chain initiation factors were prepared from the 0.5 M KCl wash of rat liver microsomes. Their activities in connection with dimethylnitrosamine (DMNA)-induced inhibition of protein synthesis were studied by use of the following reactions: (1) poly(U)-directed binding of Phe-tRNA to ribosomes, (2) formation of a GTP-dependent ternary initiation complex with Met-tRNAf, (3) binding of Met-tRNAf to 40-S ribosomal subunits, (4) assembly of a Met-tRNAf containing 80-S ribosomal initiation complex and (5) ribosome-dependent GTPase activity. The inhibition of protein synthesis with DMNA was not associated with a loss of factor activity in any of these reactions. In the binding of Met-tRNAf to 40-S subunits there was a noticeable increase, probably related to the stability of the resulting complex. The Met-tRNA deacylase activity was also increased.

Animals↗
PubMed1978

RNA metabolism and poly(A) distribution in mouse liver following administration of dimethylnitrosamine.

Dimethylnitrosamine (DMNA) strongly inhibited RNA synthesis in mouse liver under conditions when the nucleotide pattern, rate of nucleotide synthesis and phosphorylation ratio were unaffected. (An unidentified, probably non-nucleotide, component in the acid-soluble liver fraction was selectively reduced.) The inhibition of RNA synthesis was associated with a decrease in the RNA polymerase activity of isolated liver nuclei, well established already 45 min after DMNA administration. The reduced activity included both Mg2+- and Mn2+/(NH4)2SO4-stimulated polymerase functions. The inhibition in vivo involved the whole complement of RNA, including poly (A)-containing RNA and isolated poly(A) sequences. The transfer of labelled RNA from the nucleus to the cytoplasm was not impaired. There was no detachment of poly(A)-containing RNA from the microsomes, and the proportion of tightly membrane-bound microsomal RNA and poly(A) sequences was not reduced as determined by use of a flotation technique. No breakage or shortening of the poly(A) chains was indicated by sedimentation analysis.

Animals↗
PubMed1977

Accumulation of tRNAMetf on 80-S ribosomes in vitro under the influence of a Met-tRNA deacylase from rat-liver microsomes.

A Met-tRNA deacylase has been partially purified from the 0.5 M KCl wash of rat liver microsomes. In preparative sucrose gradients, the active component sediments as a single band at about 6 S, corresponding to an estimated molecular weight of 1.7 X 10(5). The deacylase is specific for Met-tRNA, without discriminating between Met-tRNA f and Met-tRNAm. Met-tRNAf bound to the initiation factor IF-MP in the ternary complex, IF-MP-GTP-Met-tRNAf, or to initiation-factor-dependent, complexes with 40-S subunits or 80-S ribosomes, is protected against deacylation. However, in the course of the initiation-factor-dependent joining of the 40-S subunit complex to 60-S ribosomal subunits, the bound Met-tRNAf is exposed to added deacylase. Under these conditions, deacylation is inhibited by GTP. The tRNAMetf remains bound and accumulates on the 80-S ribosomes.

Acyltransferases↗
PubMed1976

Separation of Met-tRNAf and Met-tRNAm by chromatography on Sepharose 4B columns.

Unfractionated rabbit liver tRNA, charged with [3H]methionine by use of rat liver enzymes, was separated into two [3H5methionine-containing fractions by column chromatography on Sepharose 4B. The two fractions were identified as Met-tRNAMetm and Met-tRNAMetf by (a) their different ability for form a GTP-dependent ternary complex with IF-MP, and (b) the absence of the first fraction after selective charging of the tRNA with E. coli amino acyl tRNA synthetase. The methionine residue was without noticeable influence on the separation.

Animals↗
PubMed1975

Protein chain initiation in vitro by liver cell components from DMNA-treated rats.

The mechanism of inhibition of protein synthesis in rat liver after dimethylnitrosamine (DMNA) administration was studied at the level of peptide-chain initiation by use of initiation-dependent amino acid incorporating systems. Ribosomal monomers, poly(A)-concontaining loss of acticity due to the DMNA treatment. The poly(A) RNA from monosomes and polysomes, and crude initiation factors from microsomes were prepared 2 h after a single dose of DMNA (75 mg/kg), and their activities in the production of new protein chains determined under conditions of nearly linear response. Monosomes and crude initiation factors from DMNA-treated rats were at least as active as those from controls. Preparations of poly(A)-containing RNA had a consistently higher template activity when prepared from polysomes instead of monosomes. However, in neither case was there any ltaining RNA was methylated by DMNA to about the same extent as the 18S and 28S rRNA. The methylation was consistently somewhat higher in the RNA preparations from monosomes than in those from polysomes.

Animals↗