Biomedical subjects
Publications and source records attributed to J Neil.
A controlled study comparing clinical aspects of birthing unit confinement with orthodox obstetric care in a major obstetric hospital is detailed. The results confirm that this centre provides an acceptable and safe alternative for those who desire such an environment.
Luminol-dependent phagocytic chemiluminescence was used to measure opsonins to group B Streptococcus type III in serum samples from pregnant women. Mean levels were similar amongst patients colonized with this organism and those who were not. Values remained fairly constant for individual women during pregnancy apart from a small, but consistant fall in cord blood samples. Again using luminol-dependent chemiluminescence, 54 clinical isolates of group B Streptococcus type III were evaluated for susceptibility to serum opsonization. Six were found to be resistant and these originated from both colonized babies and babies with systemic GBS infections. Further studies demonstrated strain-to-strain variation in the degree of dependence on both heat-labile and heat-stable opsonins.
The development of single channel recording has brought with it the need to analyse enormous amounts of data. The data analysis is time consuming and subject to observer biases since the events are random in time and are contaminated with uncorrelated noise. We have developed a heuristic pattern recognition program which identifies with high precision single channel currents and rejects contaminating noise. The program interactively provides for a variety of amplitude and duration measures. Analysis is flexible and rapid: a file containing over 10,000 events can be analysed in under 2 h. Specific detection features include variable lowpass filtering, automatic baseline restoration, and adaptive amplitude thresholds. A record is analysed through duration histograms, binomial estimates of the number of active channels present, cross-correlation estimates between parameters, spectral analysis of events and background noise, and stationarity of mean channel current. The graphic output facilities can plot raw data (after filtering and baseline restoration) with the idealized signal superimposed or with detected events underlined. A batch processing facility has been included to allow processing of data during periods of low computer demand.
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To determine if proteins RNase III and rho, both of which can determine the 3' ends of RNA molecules, can complement each other, double mutants defective in these two factors were constructed. In all cases (four rho mutations tested) the double mutants were viable at lower temperatures, but were unable to grow at higher temperatures at which both of the parental strains grew. Genetic analyses suggested that the combinations of the rnc rho (RNase III-Rho-) mutations was necessary and probably sufficient to confer temperature sensitivity on carrier strains. Physiological studies showed that synthesis and maturation of rRNA, which is greatly affected by RNase III, as well as other RNAs, was indistinguishable in rnc rho strains as compared to rnc rho+ strains, thus suggesting that RNase III and rho do not complement one another in determining the 3' ends of RNA molecules. In rnc rho strains, however, the newly synthesized rRNA failed to accumulate. Thus, decay of rRNA could be the reason for the temperature sensitivity of the double mutant strains. These experiments suggest that RNase III and rho can both protect rRNA from degradation by cellular ribonucleases. They also point to the possibility that the nucleotide sequences involved in the determination of the 3' ends of RNA molecules by these two factors are not identical.
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E. coli strains carrying the rnc-105 allele do not show any level of RNase III in extracts, grow slower than rnc+ strains at temperatures up to 45 degrees C and fail to grow at 45 degrees C. Revertants which can grow at 45 degrees C were isolated. The vast majority of them still do not grow as fast as rnc+ strains and did not regain RNase III activity. The mutation(s) which caused them are suppressor mutations (physiological suppressors) which do not map in the immediate vicinity of the rnc gene. A few of the revertants regain normal growth, and contain normal levels of RNase III. They do not harbor the rnc-105 allele and therefore are considered to be true revertants. By using purines other than adenine it was possible to isolate rnc + pur- revertants from an rnc- pur- strain with relative ease. They behaved exactly like the true rnd+ revertants isolated from rns- strains at 45 degrees C. A merodiploid strain which contains the rnc+ gene on an episome behaves exactly like an rnc+ strain with respect to growth and RNA metabolis, eventhough its specific RNase III activity is about 60% of that of an rnc+ strain; thus the level of RNase III is not limiting in the cell. The rnc- strains show a characteristic pattern of transitory molecules, related to rRNA, 30S, 25S, "p23" and 18S, which are not observed in rnc+ strains. This pattern is unchanged in rnc- strains and in the revertants which are still lacking RNase III, regardless of the temperature in which RNA synthesis was examined (30 degrees to 45 degrees C). On the other hand, in the rnc+ strains as well as in the true revertants and the rnc+/rnc- merodiploid, the normal pattern of p16 and p23 is observed at all temperatures. These findings suggest that all the effects observed in RNase III- strains are due to pleiotropic effects of the rnc-105 allele, and that the enzyme RNase III is not essential for the viability of the E. coli cell.
An isogenic pair of Escherichia coli strains, one carrying an rnc+ and the other an rnc- allele (a mutation which reduces the level of ribonuclease III), was compared. The rnc- strain fails to grow at very elevated temperatures (for E. coli) while the rnc+ strain does grow exponentially. Assaying the residual RNase III like activity in extracts of the rnc- strain at different pHs and at different temperatures suggested that this residual RNase III like activity is not due to RNase III. This raised the possibility that the rnc- strain is devoid of any RNase III activity in the cell. Comparing the decay of newly synthesized RNA and functional decay of beta-galactosidase mRNA in such strains revealed that in both strains these parameters proceed in similar rates, which suggests that RNase III is not involved in the metabolism of mRNA. During carbon starvation preexisting total RNA, as well as 23S and 16S rRNA, decay faster in the rnc- strain, thus eliminating the possibility that RNase III is the endoribonuclease which initiates the decay of rRNA during starvation (Kaplan and Apirion, 1975a).
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