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R S Cormack

Publications and source records attributed to R S Cormack.

12 recordsLinked to original sources
PubMed1992

Structural requirements for the processing of Escherichia coli 5 S ribosomal RNA by RNase E in vitro.

Processing of 9 S precursor RNA in Escherichia coli requires the endoribonuclease RNase E, which makes two cleavages to liberate p5, the immature form of 5 S rRNA. The contributions of primary and secondary structure to RNase E-mediated cleavage of 9 S RNA were investigated. The structure of the 5' domain of 9 S RNA was probed by partial ribonuclease digestion and chemical modification. Our structural analysis of 9 S RNA supports a model in which the 5' spacer domain folds into tandem hairpins so that the first processing cleavage site 5' to the 5 S moiety resides in a stretch of single-stranded residues. Site-directed mutagenesis of a cloned 9 S RNA sequence was performed and synthetic transcripts derived from a variety of such mutant templates were assayed as substrates for RNase E-dependent endonuclease activity in fractionated extracts. Partial or complete deletion of the 5 S sequence did not eliminate site-specific processing of 9 S RNA. Mutations affecting the 5' domain revealed that secondary structure upstream from the first cleavage site is important in maintaining efficient processing. However, secondary structure downstream from either cleavage site is dispensable. Our results suggest that RNase E specifically recognizes and cleaves single-stranded RNA sequences only when presented in a proper conformational context. Adjacent secondary structures appear to play a direct and critical role in the enzyme's recognition of its substrate. Additionally, it may serve to anchor single-stranded regions to ensure the availability of the RNase E cleavage sites.

Base Sequence↗
PubMed1991

Mapping ribosomal protein S20-16 S rRNA interactions by mutagenesis.

Specific ribonucleotides within the 5' domain of Escherichia coli 16 S rRNA were altered by deletion and/or substitution by site-directed mutagenesis of cloned DNA to assess the importance of these particular residues in defining the binding site for ribosomal protein S20. Gel filtration and sucrose gradient centrifugation were employed to measure the binding of ribosomal protein S20 to synthetic transcripts spanning the 5' domain of 16 S rRNA containing various alterations. In several cases, the apparent association constants for these interactions were also determined. Three essential results were obtained. First, RNA transcripts containing residues 1-402 are sufficient for high affinity S20 binding. Second, bulges at residues 250-251 and 278-280 in a stem-loop structure extending from residues 240 to 286 are critical for S20 binding, arguing that the "260 stem" directly interacts with S20 at these sites. Third, mutations in a hairpin structure spanning residues 316-337 demonstrate a strong requirement for both the specific A321*G332 bulge and for unpaired residues in the loop itself for proper S20 binding. Our results document the importance of unpaired residues in maintaining the interaction between S20 and 16 S rRNA.

Base Sequence↗
PubMed1991

Unexpected, difficult laryngoscopy: a prospective survey in routine general surgery.

A prospective study of unexpected, difficult laryngoscopy was carried out. During a 7-month period, all general surgery patients in whom the trachea was intubated were assessed; only those with obvious neck pathology were excluded. Ease or difficulty of laryngoscopy was graded by a standard method. There were no grade 4 cases and no failed intubations in a total of 1387 cases. There were significant differences in the results recorded by different individuals; this did not correlate with seniority or with the type of surgery. Four factors have been identified which help to explain these discrepancies. These findings are analysed in relation to the training of junior staff, with particular reference to obstetric anaesthesia.

Anesthesia, Obstetrical↗
PubMed1979

Awareness during surgery--a new approach.

With modern light anaesthesia the problem of awareness during surgery has defied analysis, because no physical sign reliably signals the conscious level. A test has been developed which entails direct communication with the patient at the end of surgery, noting the earliest moment after withdrawal of nitrous oxide at which he makes the appropriate response to a verbal request, the "time to correct response" (TCR). This test showed premedication with lorazepam 4 mg/70 kg to be significantly better than morphine 10 mg for ensuring unconsciousness when the main anaesthetic agent was nitrous oxide, in two groups of patients undergoing abdominal surgery (P less than 0.01). All patients who had lorazepam were able, on request, to hold up the head a few minutes after surgery. Thus the benefits of light anaesthesia were retained whilst ensuring unconsciousness.

Adult↗
PubMed1977

Respiratory effects and amnesia after premedication with morphine or lorazepam.

Lorazepam, a new benzodiazepine, was compared with morphine for premedication. Ten patients received morphine 10 mg/70 kg i.m. and 10 received lorazepam 4 mg/70 kg i.m. Respiratory effects were assessed from the change in slope (S) and intercept (B) of the carbon dioxide response line, using a development of Read's rebreathing method. Morphine depressed S by 47% (P less than 0.01), but after lorazepam S increased by 27% (P less than 0.05), neither drug altering B significantly. In two volunteers lorazepam was assessed by both the rebreathing and the steady-state methods; after lorazepam S was smaller by the steady-state than by the rebreathing technique. The findings for lorazepam are consistent with the known effects of sleep on carbon dioxide sensitivity. Amnesia lasting 4-8 h occurred in all patients who received lorazepam so that pain and nausea during this period were not recalled, but no patient who received morphine experienced amnesia. We conclude that lorazepam merits further study, particularly where sedation without respiratory depression is needed, as in obstetrics, and where amnesia for uncomfortable procedures is required.

Adolescent↗