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Biomedical subjects

S Altman

Publications and source records attributed to S Altman.

At least 91 records · Page 5Linked to original sources
PubMed1992

Subpressor angiotensin II is a bifunctional growth factor of vascular muscle in rats.

OBJECTIVE: The proposition that angiotensin II in subpressor does stimulates vascular growth in vivo was tested. DESIGN: Young adult, male Sprague-Dawley rats received angiotensin II, 200 ng/kg per min intraperitoneally by osmotic minipump, for 24 h or 7-10 days. Sham-infused rats served as controls. METHODS: Protein (35S-methionine) synthesis in aortic media, portal vein, bladder wall and diaphragm; proteoglycan (35S-sulfate) synthesis in aorta and bladder and synthesis of DNA (3H-thymidine) in aortic media were all measured ex vivo in the rat. RESULTS: The systolic blood pressure of angiotensin II-treated rats was unchanged at 24 h and increased at 7-10 days. At 24 h in angiotensin II-treated rats the protein synthesis in aortic media, portal vein and bladder wall but not in the diaphragm was increased, indicating that the hypertrophic effect of angiotensin II was independent of the arterial pressure. The rate of 35S-methionine washout from angiotensin II- and sham-treated aorta was the same. At 24 h there was also an increase in proteoglycans synthesis of the aorta and bladder wall of angiotensin II-treated rats. In contrast to protein synthesis, the incorporation of 3H-thymidine into aortic muscle DNA was reduced in angiotensin II-treated rats at 24 h, suggesting the inhibition of DNA synthesis. At 7-10 days angiotensin II administration the protein synthesis of aortic media returned to baseline, and DNA synthesis was bimodal: in 53% of rats (n = 10) inhibition continued, and in 26% (n = 5) it was increased by two- to threefold. CONCLUSIONS: The present findings confirm in vivo the bifunctionality of the trophic vascular action of angiotensin II. Vascular hypertrophy may play a role in the slow pressor action of angiotensin II.

Angiotensin II↗
PubMed1992

The incorporation of acupuncture into a small animal practice.

Successful use of acupuncture in small animal practice on a day-to-day basis depends on an organized approach. The staff must be trained to answer telephone inquiries and client questions and to obtain a good history before appointments are scheduled. Colleagues must be ethically and professionally assured of a veterinarian's acupuncture credentials and capabilities, so that they will become a source of patient referrals. A proper examination must be conducted that incorporates traditional western veterinary practices with acupuncture, and the results must be properly recorded. A diagnosis should be established before therapy is initiated, and a plan of treatment set up. The prognosis, projected costs, length of treatment regimen, other means of treating the condition, and any possible sequelae should be discussed with the client. The patient should be monitored during the course of treatment, and reevaluated to determine whether or not changes in acupuncture prescription or additional modes of therapy or supportive care are needed. Communication with the client and the referring veterinarian should be a priority.

Acupuncture Points↗
PubMed1992

Techniques and instrumentation.

There are many methods used to stimulate acupuncture points to achieve therapeutic objectives. Among the most frequently employed are physical pressure or vacuum (acupressure and cupping), temperature variation (cauterization, moxibustion, electronic heat devices, infrared lamps, ultraviolet lights, ice, dry ice, and surface coolants such as ethyl chloride), ultrasound (sonapuncture), injection therapy (aquapuncture), implantation of various materials into points, laser stimulation (laserpuncture), and electrostimulation of the acupuncture points, with or without needles (electroacupuncture). This chapter describes these techniques, their uses, and place in acupuncture therapy.

Acupuncture Therapy↗
PubMed1991

Multiple cis-acting elements are required for RNA polymerase III transcription of the gene encoding H1 RNA, the RNA component of human RNase P.

In humans, the H1 RNA, the RNA subunit of RNase P, is synthesized by RNA polymerase III. We have used block replacement mutagenesis to identify the sequences necessary for in vitro transcription of H1 RNA. We find that multiple cis-acting elements located in the H1 RNA 5'-flanking region are necessary for H1 RNA synthesis; no internal sequences are essential. Required cis-acting elements include sequences resembling proximal sequence element, distal sequence element, and TATA motifs. In this respect, the H1 RNA promoter is similar in structure to the promoters of the genes encoding the U6 snRNA, the 7 SK RNA and the MRP RNA. However, our mutational analysis indicates that the H1 promoter is unexpectedly complex, with several additional cis-acting elements spanning nearly 70 base pairs of the H1 RNA gene 5'-flanking sequence.

Base Sequence↗
PubMed1991

Site-specific cleavage by metal ion cofactors and inhibitors of M1 RNA, the catalytic subunit of RNase P from Escherichia coli.

The location of phosphate residues involved in specific centers for binding of metal ions in M1 RNA, the catalytic RNA subunit of RNase P from Escherichia coli, was determined by analysis of induction of cleavage of RNA by metal ions. At pH 9.5, Mg2+ catalyzes cleavage of M1 RNA at five principal sites. Under certain conditions, Mn2+ and Ca2+ can each replace Mg2+ as the cofactor in the processing of precursor tRNAs by M1 RNA and P RNA, the RNA subunit of RNase P from Bacillus subtilis. These cations, as well as various metal ion inhibitors of the catalytic activity of M1 RNA, also promote cleavage of M1 RNA in a specific manner. Certain conditions that affect the catalytic activity of M1 RNA also alter the rate of metal ion-induced cleavage at the various sites. From these results and a comparison of cleavage of M1 RNA with that of a deletion mutant of M1 RNA and of P RNA, we have identified two different centers for binding of metal ions in M1 RNA that are important for the processing of the precursor to tRNA(Tyr) from E. coli. There is also a center for the binding of metal ions in the substrate, close to the site of cleavage by M1 RNA.

Bacillus subtilis↗
PubMed1991

Kinetics of the processing of the precursor to 4.5 S RNA, a naturally occurring substrate for RNase P from Escherichia coli.

A study was made of the cleavage by M1 RNA and RNase P of a non-tRNA precursor that can serve as a substrate for RNase P from Escherichia coli, namely, the precursor to 4.5 S RNA (p4.5S). The overall efficiency of cleavage of p4.5S by RNase P is similar to that of wild-type tRNA precursors. However, unlike the reaction with wild-type tRNA precursors, the reaction catalyzed by the holoenzyme with p4.5S as substrate has a much lower Km value than that catalyzed by M1 RNA with the same substrate, indicating that the protein subunit plays a crucial role in the recognition of p4.5S. A model hairpin substrate, based on the sequence of p4.5S, is cleaved with greater efficiency than the parent molecule. The 3'-terminal CCC sequence of p4.5 S may be as important for cleavage of this substrate as the 3'-terminal CCA sequence is for cleavage of tRNA precursors.

Base Sequence↗
PubMed1990

External guide sequences for an RNA enzyme.

Ribonuclease P (RNase P) from Escherichia coli or its catalytic RNA subunit can efficiently cleave small RNA substrates that lack the conserved features of natural substrates of RNase P if an additional small RNA is also present. This additional RNA must contain a sequence complementary to the substrate [external guide sequence (EGS)] and a 3'-proximal CCA sequence to ensure cleavage. The aminoacyl acceptor stem and some additional 5'- and 3'-terminal sequences of a precursor transfer RNA are sufficient to allow efficient cleavage by RNAase P, and the 2'-hydroxyl group at the cleavage site is not absolutely necessary for cleavage. In principle, any RNA could be targeted by a custom-designed EGS RNA for specific cleavage by RNase P in vitro or in vivo.

Base Sequence↗
PubMed1990

Interaction of RNase P from Escherichia coli with pseudoknotted structures in viral RNAs.

In a previous study it was shown that RNase P from E. coli cleaves the tRNA-like structure of turnip yellow mosaic virus (TYMV) RNA in vitro (Guerrier-Takada et al. (1988) Cell, 53, 267-272). Cleavage takes place at the 3' side of the loop that crosses the deep groove of the pseudoknot structure present in the aminoacyl acceptor domain. In the present study fragments of TYMV RNA with mutations in the pseudoknot, generated by transcription in vitro, were tested for susceptibility to cleavage by RNase P. Changes in the specificity with respect to the site of cleavage and decreases in the rate of cleavage were observed with most of these substrates. The behaviour of various mutants in the reaction catalyzed by RNase P is in agreement with the present model of the TYMV RNA pseudoknot (Dumas et al. (1987), J. Biomol. Struct. Dyn. 263, 652-657). Base substitutions in the loop that crosses the shallow groove of the pseudoknot structure resulted, however, in an unexpected decrease in the rate of cleavage, probably due to conformational changes in the substrates. Studies on other tRNA-like structures revealed an important role in the reaction with RNase P for both the nucleotide at the 3' side of the loop that spans the deep groove and the nucleotide at position 4, which correspond to positions--1 and 73, respectively, in tRNA precursors.

Base Sequence↗
PubMed1990

Structure and transcription of a human gene for H1 RNA, the RNA component of human RNase P.

The gene coding for H1 RNA, the RNA component of human RNase P, has been isolated and characterized from a human genomic DNA library. The sequence corresponding to the mature H1 RNA is almost identical to that previously identified using H1 RNA and a cDNA clone corresponding to it. The nucleotide sequence of the genomic clone contains an array of potential transcriptional control elements, some characteristic of transcription by RNA polymerase III and some characteristic of RNA polymerase II, as is also the case for U6 and certain other small stable RNAs. The transcription in vitro of the genomic clone shows that the gene is functional and is transcribed by RNA polymerase III. Southern hybridization analysis indicates that there is very likely only one copy of the gene for H1 RNA in the human genome.

Base Sequence↗
PubMed1990

Protection from chemical modification of nucleotides in complexes of M1 RNA, the catalytic subunit of RNase P from E coli, and tRNA precursors.

Certain nucleotides in M1 RNA, the catalytic RNA subunit of RNase P from E coli, are protected from chemical modification when M1 RNA forms complexes with tRNA precursor molecules (ES complexes). Many of these nucleotides are important in the formation of the Michaelis complex. In the presence of tRNA precursor molecules, the pattern of protection from chemical modification of a region in M1 RNA that resembles the E site in 23S rRNA is similar to the pattern of protection of the E site in the presence of deacylated tRNA. In the complex with the RNA enzyme, more nucleotides in the substrate become accessible to modification, an indication that the substrate is in an unfolded conformation under these conditions.

Base Sequence↗
PubMed1989

Specific interactions in RNA enzyme-substrate complexes.

Analysis of crosslinked complexes of M1 RNA, the catalytic RNA subunit of ribonuclease P from Escherichia coli, and transfer RNA precursor substrates has led to the identification of regions in the enzyme and in the substrate that are in close physical proximity to each other. The nucleotide in M1 RNA, residue C92, which participates in a crosslink with the substrate was deleted and the resulting mutant M1 RNA was shown to cleave substrates lacking the 3' terminal CCAUCA sequence at sites several nucleotides away from the normal site of cleavage. The presence or absence of the 3' terminal CCAUCA sequence in transfer RNA precursor substrates markedly affects the way in which these substrates interact with the catalytic RNA in the enzyme-substrate complex. The contacts between wild-type M1 RNA and its substrate are in a region that resembles part of the transfer RNA "E" (exit) site in 23S ribosomal RNA. These data demonstrate that in RNA's with very different cellular functions, there are domains with similar structural and functional properties and that there is a nucleotide in M1 RNA that affects the site of cleavage by the enzyme.

Base Sequence↗