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Biomedical subjects

S Altman

Publications and source records attributed to S Altman.

At least 163 records · Page 9Linked to original sources
PubMed1980

Identification of ribonuclease P activity from chick embryos.

RNAase P (EC 3.1.26.5) activity has been identified in chick embryo thigh tissue on the basis of specific cleavage of Escherichia coli 129 nucleotide tRNATyr precursor and has been partially purified by the procedure used for human tissue culture KB cell RNAase P. RNAase P from chick resembles the KB cell RNAase P in substrate specificity, requirement for a divalent cation (Mg2+) and a monovalent cation (K+, Na+ or NH4+) for activity, inhibition by bulk tRNA, ready inactivation by proteases, and increasing instability; with purification. RNAase P activity is also present in whole chick embryos, as well as in liver and heart tissues. Furthermore, crude preparations of RNAase P from chick embryo heart tissue are relatively free of contaminating nucleases.

Animals↗
PubMed1980

E. coli RNAase P has a required RNA component.

RNAase P has been partially purified from three thermosensitive strains of E. coli and the thermal inactivation characteristics of each preparation have been determined. The RNAase P preparations from two of these mutant strains, ts241 and ts709, and the wild-type strain have been separated into RNA and protein components. Various mixtures of the reconstituted components have been checked in vitro for complementation of their thermal sensitivity properties. The protein component of RNAase P from ts241 and the RNA component of RNAase P from ts709, respectively, account for the thermal sensitivity of the rnaase P from the two strains. The amount of the RNA component of RNAase P is lower in ts709 than in ts241 or the wild-type parent, 4273. RNAase P partially purified from a revertant of the third mutant strain, A49, which maps at or near the ts241 mutation, has an altered charge when compared to the RNAase P from the parent strain, BF265. We conclude that mutations which affect either the protein or RNA component of RNAase P can confer thermal sensitivity on the enzyme both in vivo and in vitro.

Escherichia coli↗
PubMed1979

Respiratory and cardiac arrest under general anaesthesia: treatment by acupuncture of the nasal philtrum.

The philtrum point VG 26 (Jen Chung) was needled in 69 cases of respiratory depression or apnoea in dogs and cats during induction or maintenance of general anaesthesia. Respiration was restored to normal or near normal rates within 10 to 30 seconds of insertion of the needle in all the cases. In seven cases of anaesthetic apnoea with concurrent cardiac arrest and absence of vital signs, the revival rate was 43 per cent. Those which recovered required four to 10 minutes of acupuncture stimulation. In eight cases of collapse due to other causes, the revival rate was 25 per cent. The cases included five sheep in shock following liver biopsy, two cases of haemorrhagic shock (dog, cat) and one terminal collapse in chronic congestive heart failure (dog).

Acupuncture Therapy↗
PubMed1979

In vitro processing of B. mori transfer RNA precursor molecules.

Ribonuclease P and 3'-5' nuclease, two enzymatic activities necessary for tRNA synthesis in E. coli, are also found in the silkgland cells of Bombyx mori. B. mori subcellular extracts containing RNAase P activity can cleave the E. coli tRNA precursor molecule endonucleolytically at the same site as the E. coli enzyme, and will also cleave in vitro all E. coli tRNA precursors (pre-tRNAs) which the bacterial enzyme recognizes. B. mori RNAase P will not cleave two E. coli RNAase P substrates that are structurally unrelated to tRNA. Pre-tRNAs from B. mori contain extra 5' and 3' nucleotides as judged by RNA fingerprinting and 5' terminal phosphate analysis. Crude silkgland extracts containing both RNAase P and 3'-5' nuclease can remove the 5' and 3' extra nucleotides from B. mori pre-tRNAs, whereas purified fractions containing RNAase P remove only 5' extra nucleotides. Only large silkworm pre-tRNAs were found to be susceptible to cleavage by B. mori RNAase P. This observation and sequence analysis of intermediates of in vitro processing reactions indicate a two-step process of pre-tRNA maturation in which extra 5' nucleotides are first removed by RNAase P and extra 3' nucleotides are then trimmed off by a 3'-5' nuclease.

Animals↗
PubMed1979

Reconstitution of RNase P activity from inactive RNA and protein.

RNase P preparations from Escherichia coli can be separated into RNA and protein by chromatography, in buffers containing 7 M urea, on Sephadex G-200, DEAE-Sephadex, or CM-Sephadex columns. Neither RNA nor protein components alone exhibits any RNase activity. RNase P activity can be reconstituted by mixing separated RNA and protein components in buffer containing 7M urea followed by dialysis of this mixture to remove the urea. Of several purified RNAs tried, only M2 RNA, the RNA species found in purified RNase P, is active in the reconstitution experiments.

Escherichia coli↗
PubMed1978

Identification of precursor molecules to individual tRNA species from Bombyx mori.

Short-labeled 4.5S RNA molecules isolated from the posterior silk gland of Bombyx mori can be separated by two-dimensional polyacrylamide gel electrophoresis into many discrete species, some of which are radiochemically pure by the criteria of RNA fingerprinting. One region of the gel contains two precursor RNAs, one to each of the known alanine transfer RNAs. Each precursor tRNAAla molecule contains all of the internal oligonucleotides present in the corresponding tRNAAla species plus new 5'-and 3'-terminal sequences. Precursor molecules to tRNA1Gly (which differ from each other in size) are contained in two other gel regions, and a fourth region contains a precursor to tRNA2Gly. Both of the transcription initiator purine tetraphosphate nucleosides are present in unfractionated tRNA precursor mixtures, with pppA- predominating over pppG-. Minor nucleotides are also present in B. mori tRNA precursors. No polycistronic tRNA gene transcripts were observed.

Alanine↗
PubMed1978

Ribonuclease P: an enzyme with an essential RNA component.

The activity of ribonuclease P on precursor tRNA substrates from Escherichia coli can be abolished by pretreatment of this enzyme with micrococcal nuclease or pancreatic ribonuclease A, as well as by proteases and by thermal denaturation. Highly purified RNase P exhibits one prominent RNA and one prominent polypeptide component when examined in polyacrylamide gels containing sodium dodecyl sulfate. The buoyant density in CsCl of RNase P, 1.71 g/ml, is characteristic of a protein-RNA complex. The activity of RNase P is inhibited by various RNA molecules. The presence of a discrete RNA component in RNase P appears to be essential for enzymatic function. A model is described for enzyme-substrate recognition in which this RNA component plays an important role.

Chemical Phenomena↗
PubMed1978

Context effects on nonsense codon suppression in Escherichia coli.

The influence of mRNA context on nonsense codon suppression has been studied by suppression measurements at one site in the Escherichia coli trpE gene and at two sites in the trpA gene. The ratio of suppression efficiencies of amber and ochre codons at each site (homotopic pairs) has been compared using ochre suppressing derivatives of tRNATyr. This ratio is independent of differential effects of the inserted amino acid on enzyme function. We have found that mRNA context can change the ratio of suppression efficiencies of homotopic nonsense codons at the three sites in the trp gene system over a ten-fold range. The causes of such variation, and, in particular the effect of certain adjacent nucleotides on nonsense codon suppression are considered.

Anthranilate Synthase↗
PubMed1978

Endoribonuclease activity associated with animal RNA viruses.

A specific endoribonucleolytic activity was detected when detergent-lysed vesicular stomatitis of Sendai virus was incubated with the precursor to Escherichia coli tRNA Tyr. The cleavage products produced and the characteristics of the reaction were similar to those previously reported for human KB cell RNase NU. Like RNase NU, the virus-associated reaction generates 5'-hydroxyl and 3'-phosphate groups at the cleavage sites. At protein concentrations similar to those used to test vesicular stomatitis and Sendai viruses, virions of Sindbis virus and poliovirus also exhibited endoribonucleolytic activity, but reovirus, simian virus 40, and minute virus of mice did not. This endoribonuclease may be of physiological relevance to some of the viruses we tested.

Cell-Free System↗
PubMed1976

Nucleotide sequence and in vitro processing of a precursor molecule to Escherichia coli 4.5 S RNA.

A precursor molecule to the stable 4.5 S RNA species of Escherichia coli has been found to accumulate at 42 degrees in a strain thermosensitive for the function of ribonuclease P. The precursor molecule is 130 nucleotides long. Twenty-two extra nucleotides, starting with pppGp, precede the mature sequence at its 5' terminus. At least 1 extra uridine residue can be found at the 3' terminus. The precursor to 4.5 S RNA is cleaved in vitro by RNase P to generate a 5' end identical to that of the mature 4.5 S RNA.

Base Sequence↗
PubMed1976

Identification of a ribonuclease P-like activity from human KB cells.

An endoribonuclease which cleaves tRNA precursor molecules has been partially purified from human KB tissue culture cells. This activity is found in cytoplasmic fractions but is not detectable in the nucleoplasm. tRNA precursor molecules from both E. coli and KB cells are cleaved by this novel activity to produce 5' phosphate-terminated oligonucleotides. E coli RNAase P and the KB cell nuclease both make a single endonucleolytic scission in E. coli tRNATyr precursor, thereby separating the 41 extra nucleotides on the 5' end of the precursor molecule from the 5' terminal sequence of the mature tRNATyr molecule. The cleavage products generated from other E. coli tRNA precursors by the KB cell activity are identical in size to those produced by RNAase P. The KB cell endoribonuclease requires Mg2+ and a monovalent cation (Na+, K+, or NH4+) for function. The enzymatic activity has a broad pH optimum, centered near pH 8.0, and the activity is inhibited by tRNA. Several KB cell RNAs with long half-lives in vivo, including 5S and bulk 4S RNA, are not cleaved by this nuclease. The KB cell endoribonuclease resembles E. coli RNAase P in its substrate specificity, pH optimum, ion requirements, and sensitivity to tRNA. These properties and the cytoplasmic localization of the novel endoribonuclease indicate its involvement in the biosynthesis of KB cell tRNA.

Ammonia↗