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Biomedical subjects

S Altman

Publications and source records attributed to S Altman.

At least 127 records · Page 7Linked to original sources
PubMed1987

Relation of serum total cholesterol and high-density lipoprotein cholesterol percentage to the incidence of definite coronary events: twenty-year follow-up of the Donolo-Tel Aviv Prospective Coronary Artery Disease Study.

This 20-year follow-up report presents the incidence of definite coronary events and its relation to serum total cholesterol (TC) and alpha-lipoprotein cholesterol percentage (percentage of serum TC bound with alpha-lipoprotein), now usually called high-density lipoprotein cholesterol percentage (HDL-C%). The cohort consists of 1,454 men and 1,481 women, presumably healthy, aged 35 to 64 years at the time of entrance examination in 1964. During the follow-up period 123 men and 44 women died from coronary disease. Ninety-six men and 42 women had nonfatal myocardial infarctions. The incidence of definite coronary events increased from 6% in men with TC levels of less than 200 mg/dl to 25% in men with levels of more than 264 mg/dl. The corresponding figures in women were 3% and 10%. The incidence of definite coronary events was inversely correlated to HDL-C%. The incidence of definite coronary events in 225 men with HDL-C% of less than 14% was 28%, and in 669 men with HDL-C% of 21% or more, 7%. The corresponding figures in 234 women with HDL-C% of less than 17% was 14%, and in 853 women with HDL-C% of 23% or more, 2%. Two HDL-C% subsets were assessed: "low" and "high" subsets refer to HDL-C% of less than 21% and 21% or more, respectively, in men and less than 23% and 23% or more in women.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Role in translation of a triple tandemly repeated sequence in the 5'-untranslated region of human thymidylate synthase mRNA.

A triple tandem repeat (TTR) consisting of 90 nucleotides exists immediately upstream of the ATG initiator codon in human thymidylate synthase (TS) cDNA (pcHTS-1). To investigate the role of the TTR in the expression of the TS cDNA, we used pcHTS-1 to construct mutant cDNA clones in which part of the TTR was deleted or an additional element was inserted. The mutant cDNA plasmid was introduced into murine TS-negative mutant cells and the relative translation efficiencies of the mutant cDNAs were determined by measuring the transient expression of TS activity and the amount of TS mRNA transcribed. The translation efficiency in transient expression of the mutants was increased by deletions covering all the first two repeated elements, and the part of the third closest to the ATG initiator codon, but was not affected by deletions of only parts of the first two repeated elements at the 5' end. The translation efficiency was also not affected by insertion of an additional repeated element into the TTR. These results suggest that the first two repeated elements at the 5' end both have inhibitory effects on translation of the TS mRNA, probably due to the unique structural feature of this element.

Animals↗
PubMed1987

Suppressor and novel mutants of bacteriophage T4 tRNA(Gly).

We have isolated a weak UGA suppressor of phage T4 tRNA(Gly) in which the anticodon is changed from UCC to UCA. Two secondary mutants lacking suppressor activity are atypical in accumulating tRNA(Gly). Both mutations change the T stem of the cloverleaf model. One involved a G to A change at the 5' base position of the middle base-pair; the second involves a C to U change at a constant base position next to the T loop. The precursor RNAs of the mutants were cleaved in vitro with the catalytic RNA subunit of RNase P. Relative to normal precursor RNA, the precursor mutated at the middle base-pair position of the T stem was cleaved more rapidly, whereas the precursor mutated at the base-pair position next to the T loop was cleaved more slowly.

Base Sequence↗
PubMed1987

Heterologous enzyme function in Escherichia coli and the selection of genes encoding the catalytic RNA subunit of RNase P.

The gene for the catalytic RNA subunit of RNase P has been isolated from several Enterobacteriaceae by complementation of an Escherichia coli strain that is temperature-sensitive for RNase P activity. The selection procedure relies on the ability of the heterologous gene products to function enzymatically in E. coli. This procedure obviates the need for positive results in DNA blot hybridization experiments or for the purification of holoenzyme to identify the RNA component of RNase P and its corresponding gene from organisms other than E. coli. Comparisons of the variations in sequences provide the basis for a refined two-dimensional model of the secondary structure of M1 RNA.

Base Sequence↗
PubMed1986

Site-directed mutagenesis of M1 RNA, the RNA subunit of Escherichia coli ribonuclease P. The effects of an addition and small deletions on catalytic function.

One addition mutation and several small deletion mutations have been created in vitro at a unique site in the gene coding for M1 RNA, the RNA subunit of Escherichia coli RNase P. The mutant genes exhibit a wide range of efficiencies in complementing another mutant that is thermosensitive for RNase P function in vivo. The transcripts of the mutated genes cleave a precursor tRNA in vitro with efficiencies that parallel their ability to function in the complementation assay in vivo. The secondary structures in solution of the mutant gene transcripts are shown to be different from the parent molecule by probing the structure of the transcripts with ribonuclease T1. A local region of secondary structure, between nucleotides 275 and 295, must be maintained for normal function of M1 RNA.

Endoribonucleases↗
PubMed1986

M1 RNA with large terminal deletions retains its catalytic activity.

Truncated transcripts of the rnpB gene from E. coli, coding for M1 RNA, the catalytic subunit of RNAase P, and fragments of M1 RNA generated by nuclease treatment have been prepared, and their ability to function catalytically in vitro has been determined. Molecules missing as many as 122 nucleotides at the 3' terminus retain catalytic activity, although at a much lower level than M1 RNA itself. No activity is observed with an RNA that is missing 70 nucleotides at the 5' terminus. The removal of even a small number of nucleotides from both termini eliminates all catalytic function. The preservation of one intact terminus may be essential for the tertiary and quaternary interactions required to generate the conformation of an active RNA species.

Bacterial Proteins↗
PubMed1986

Metal ion requirements and other aspects of the reaction catalyzed by M1 RNA, the RNA subunit of ribonuclease P from Escherichia coli.

M1 RNA, the RNA subunit of ribonuclease P from Escherichia coli, can under certain conditions catalytically cleave precursors to tRNA in the absence of C5, the protein moiety of RNase P. M1 RNA itself is not cleaved during the reaction, nor does it form any covalent bonds with its substrate. Only magnesium and, to a lesser extent, manganese ions can function at the catalytic center of M1 RNA. Several other ions either inhibit the binding of magnesium ion at the active site or function as structural counterions. The reaction rate of cleavage of precursors to tRNAs by M1 RNA is enhanced in the presence of poly-(ethylene glycol) or 2-methyl-2,4-pentanediol. Many aspects of the reaction catalyzed by M1 RNA are compatible with a mechanism in which phosphodiester bond cleavage is mediated by metal ion.

Binding Sites↗
PubMed1986

M1 RNA, the RNA subunit of Escherichia coli ribonuclease P, can undergo a pH-sensitive conformational change.

After purification from extracts of whole cells, M1 RNA, the catalytic subunit of ribonuclease P from Escherichia coli, apparently must undergo a change in conformation before it can function catalytically. The rate of this conformational change is dependent upon the duration of incubation at various temperatures and pH. delta E of the transition at pH 7.5 is approximately 36 kcal/mol. The change in conformation is not sensitive to Mg2+ concentration between 10 and 100 mM. A decrease in A260 of M1 RNA in solution has been observed during the incubation period that potentiates the conformational change at 30 degrees C, but no direct correlation can yet be made to specific structural rearrangements.

Endoribonucleases↗
PubMed1986

Reconstitution of RNAase P activity using inactive subunits from E. coli and HeLa cells.

HeLa cell RNAase P activity found in the flow-through of anti-Sm affinity columns can be separated into inactive RNA and protein components. These components can be used to reconstitute active hybrid enzyme complexes with purified subunits from E. coli RNAase P. The RNA in the HeLa cell fractions employed is enriched for species between 85 and 115 nucleotides long. This reconstitution assay is a convenient means of purifying the functional RNA and protein of HeLa cell RNAase P. Probes derived from the genes for the subunits of E. coli RNAase P hybridize to genomic DNA of gram-negative prokaryotic organisms, but no positive signals are seen with genomic DNA from a variety of eukaryotic organisms.

Endoribonucleases↗
PubMed1986

Affinity chromatography with an immobilized RNA enzyme.

M1 RNA, the catalytic subunit of Escherichia coli RNase P, has been covalently linked at its 3' terminus to agarose beads. Unlike M1 RNA, which is active in solution in the absence of the protein component (C5) of RNase P, the RNA linked to the beads is active only in the presence of C5 protein. Affinity chromatography of crude extracts of E. coli on a column prepared from the beads to which the RNA has been crosslinked results in the purification of C5 protein in a single step. The protein has been purified in this manner from cells that contain a plasmid, pINIIIR20, which includes the gene that codes for C5 protein. A 6-fold amplification of the expression of C5 protein is found in these cells after induction as compared to cells that do not harbor the plasmid.

Chromatography, Affinity↗
PubMed1986

Different cation transport inhibitor in benign and malignant experimental renal hypertension.

The role of circulating humoral agents in the pathogenesis of abnormal vascular wall cation composition in benign and malignant renal hypertension was investigated. Male F344 rats with chronic benign (n = 38) and malignant (n = 44) one-kidney, one clip (1K1C) hypertension and normotensive control rats (n = 63) were studied. Malignant hypertension developed spontaneously and was characterized by failure to thrive, weight loss, oedema, renal insufficiency, anaemia or haemoconcentration and hyperkalaemia. For bio-assay, monolayers of quiescent vascular smooth muscle cells from F344 rats were incubated in plasma or plasma extracts of normotensive and hypertensive rats for measurement of labelled rubidium (86Rb) uptake in the presence and absence of 2 mmol/l ouabain and/or 1 mmol/l furosemide. Compared with controls, ouabain-sensitive Rb uptake of cells was reduced in plasma extracts but not in whole plasma of rats with benign hypertension. Ouabain-sensitive Rb uptake was unchanged and ouabain-insensitive Rb uptake was reduced in both plasma and plasma extracts of rats with malignant hypertension. The latter was due to a reduction in furosemide-sensitive Rb uptake. In malignant hypertension, the increased sodium (Na) content of the aorta which characterizes benign hypertension was reversed and bladder wall Na content was reduced. The findings suggest that in malignant hypertension a circulating, furosemide-like inhibitor of ouabain-insensitive cation transport is the cause of vascular wall Na depletion and of diuresis and natriuresis that trigger the syndrome.

Animals↗
PubMed1986

Cell growth and sodium content in the serum of uninephrectomized and renal hypertensive dogs.

The long-term cellular metabolic effects of serum factors from renal hypertensive and uninephrectomized normotensive dogs were investigated. Mouse fibroblastic L cells were cultured in M199 tissue culture medium supplemented (to 15%) with serum obtained from dogs before and after the induction of one-kidney one wrapped hypertension or with serum obtained from normotensive dogs before and after unilateral nephrectomy. At confluency, the protein, water (3-O-methyl-14C-D-glucose space), Na, K, and Mg content and 3H-thymidine uptake of cells were measured. Growth curves were derived for cells growing in serum obtained before and after uninephrectomy from normotensive and hypertensive dogs. Postnephrectomy serum from both normotensive and hypertensive dogs resulted in increased recovery of protein, increased water, K, and Mg content of cells, and increased cell numbers. 3H-thymidine uptake at confluency in postnephrectomy serum was the same as in prenephrectomy serum. The one important qualitative difference between postnephrectomy serum from normotensive and hypertensive dogs was the reduced Na content and concentration of cells cultured in the serum of hypertensive dogs. The growth-promoting serum factor in postnephrectomy blood was detected for up to 8 weeks after uninephrectomy; therefore, it did not appear to be renotropin. In experimental renal hypertension, there appear to be previously unidentified serum factors that enhance transmembrane Na gradient.

Animals↗
PubMed1985

Characterization of an RNase P activity from HeLa cell mitochondria. Comparison with the cytosol RNase P activity.

A ribonuclease P-like activity was partially purified from HeLa cell mitochondria by DEAE-cellulose and octyl-Sepharose chromatography. RNase P-like activity can be quantitatively recovered from intact mitochondrial preparations treated with micrococcal nuclease, strongly suggesting that the enzyme is localized within the organelles. Mitochondrial RNase P (mtRNase P) cleaves the precursor to Escherichia coli suppressor tRNATyr at the same site as E. coli RNase P, producing the mature 5'-end of tRNATyr. The sensitivity of mtRNase P to pretreatment with nucleases or Pronase indicates that the enzyme has essential RNA and protein components. Although the ionic requirements of mtRNase P are similar to those of the RNase P activity isolated from the post-mitochondrial cytosol fraction, the chromatographic properties of mtRNase P are distinct. Mitochondrial RNase P is probably a part of the mitochondrial RNA processing machinery of mammalian mitochondria, being responsible for the endonucleolytic cleavage of the RNA transcripts at the 5'-side of the tRNA sequences.

Adenosine Triphosphate↗
PubMed1985

A catalytic RNA and its gene from Salmonella typhimurium.

The gene for the RNA subunit (M1 RNA) of ribonuclease P from Salmonella typhimurium directs the synthesis of an RNA that can cleave transfer RNA precursor molecules. The mature M1 RNA coded for by Salmonella typhimurium is 375 nucleotides long and has six nucleotide changes in comparison to M1 RNA from Escherichia coli. The regions for promotion and termination of transcription are closely conserved, but adjacent regions of nucleotide sequences show considerable drift.

Base Sequence↗
PubMed1985

Novel non-suppressing mutants of Escherichia coli tRNATyr su+3.

Several addition and deletion mutations were constructed in the region of the gene for Escherichia coli tRNATyr su+3 corresponding to the dihydrouracil loop of the mature tRNA. None of these resulting mutants had detectable suppressor function compared to the parent gene yet some directed the synthesis of mature tRNA. These latter mutants may affect the ability of the tRNA to be aminoacylated or to interact with the translational machinery on the ribosome.

Chromosome Deletion↗
PubMed1984

Structure in solution of M1 RNA, the catalytic subunit of ribonuclease P from Escherichia coli.

The structure of M1 RNA, the RNA component of Escherichia coli RNase P, has been probed by mild digestion with a variety of ribonucleases. The results have been used to generate a model for the two-dimensional structure of M1 RNA. This model is similar in many respects to an earlier model that was based entirely on theoretical considerations. M1 RNA was digested with RNase T1 in buffer containing 10 mM MgCl2 (in which M1 RNA, by itself, has no catalytic activity) and in buffer containing 60 mM MgCl2 (in which M1 RNA can cleave precursors to tRNA molecules). Under these conditions, the main features of the secondary structure are similar, but several minor differences are apparent. Such subtle changes in structure are also observed when M1 RNA is present in a binary complex with a substrate molecule, the precursor to E. coli tRNATyr.

Endoribonucleases↗