Biomedical subjects
Publications and source records attributed to N Watson.
Mutants of Escherichia coli deficient in ribonuclease III are nonmotile. All transductants and revertants that regained ribonuclease III also regained motility, and all transductants that remained or became rnc are nonmotile, although only some of the revertants that regained motility also became ribonuclease III+.
Radionuclide angiography and static whole body imaging performed with technetium-99m-labeled particulates can clearly demonstrate differential shunting in patients with patent ductus arteriosus (PDA) with Eisenmenger physiology. The anatomic arterial relationships in this condition which direct deoxygenated blood into the lower body (differential cyanosis) produce specific radionuclide images characterized by differential shunting of the technetium-99m-labeled particulates into the abdomen and lower extremity.
A comparison of isogenic RNase III+ and RNase III- strains of Escherichia coli shows that although both synthesize precursor and mature 16 S and 23 S ribosomal RNAs, the transient rRNA species of the RNase III- strain differ from those of the RNase III+ strain. The RNase III+ strain synthesizes p16 and p23 rRNA, whereas the RNase III- strain produces unstable 17 S, 18 S, "p23," 25 S and 30 S RNA molecules. The 30 S RNA, which is a primary transcript of the ribosomal RNA gene cluster, does not contribute significantly to any of the smaller RNAs, nor is m23 rRNA derived from 25 S but rather from "p23" RNA. Mature 16 S rRNA is derived from both 18 S and 17 S RNA, and 17 S RNA can be derived from 18 S. Additionally, an unstable RNA species about 300 bases long is missing in the RNase III- strain and another species which seems to be about 50 bases larger appears. Processing of the primary ribosomal RNA transcript in RNase III- strains of Escherichia coli is accomplished during its transcription by two independent pathways which are not so utilized in RNase III+ strains. One pathway yields 18 S and precursor 23 S RNAs which are processed to mature rRNAs; the second pathway yields 25 S RNA and perhaps 16 S rRNA. The second pathway, unlike the first, is inhibited by chloramphenicol treatment. At slow rates of ribosomal RNA synthesis, the nascent transcript is processed preferentially by the first pathway. We suggest that in the absence of RNase III, which is involved in the primary processing of rRNA in E. coli, other enzymes involved in primary and secondary processing of rRNA in RNase III+ cells can recognize their sites on the nascent rRNA transcript and accomplish the primary processing.
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.
A temperature sensitive mutant of Escherichia coli which fails to recover from prolonged carbon starvation, was found to be irreversibly killed by exposure to a nonpermissive temperature (43 degrees C), with a half-life of about half an hour. This bacteriocidal effect of the temperature could be reversed by a number of antibiotics which block protein synthesis but not by blocking DNA synthesis. At the nonpermissive temperature, RNA and the protein synthetic capacities decrease before the DNA synthetic capacity is decreased. Analysis of ribosomal proteins and methylation of them did not reveal any consistent differences between the parental and mutant strains. Analysis of the ribosomal RNA revealed that it is being synthesized in similar amounts as in the parental strain at the nonpermissive temperature, however, after chase its level is decreased. Moreover, the 17S precursor RNA is slow to mature to 16S rRNA in the mutant strain at the nonpermissive temperature. Thus, these studies suggest that the mutation studied here affects a late maturation step in the synthesis of the rRNA. Therefore the gene is designated rimH (for ribosomal modification). All the properties bestowee on the mutant strain are caused by a single pleiotropic mutation which maps at min 14 of the E. coli map. Three point transduction crosses suggest the order rimH, leuS, RNA, LIP. This gene maps outside the two known clusters for ribosomal structural genes.
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).
A study was made of the pattern of spinal cord injury in the elderly who are forming an ever-increasing proportion of our population. It was noted that the elderly patients had a higher incidence of cervical injuries than other age-groups with a much lower incidence of dorsal and lumbar injuries. The mortality rate in complete cervical injuries was very high but in incomplete cervical injuries and those at a lower level the majority survived the acute phase. The cause of death in the acute phase was similar to that of other age-groups. The majority of survivors were able to be discharged to their own homes to the care of relatives and they fared better then those who had to be transferred to long term geriatric hospitals. Most of the late deaths occurred within five years of discharge from hospital but a few survived over ten years. The causes of the accidents were mostly falls at home and less frequently road traffic accidents.
The potassium salt of carrageenan was found to be an adequate replacement for agar in solid bacteriological media. The common microbial genetic techniques, such as purifying colonies by streaking, replication tests, and titration of cultures, were carried out sucessfully with a number of mutant strains of Escherichia coli.
Pairs of very closely related Escherichia coli strains were prepared, one having the wild-type allele for ribonuclease III, an enzyme which specifically degrades double-stranded RNA, and the other having a mutant RNase III allele. Growth and phage plating efficiency were compared in these strains. The RNase III+ strains grow better than the RNase III- strains and plate T7 and lambda phage better, but T4 plates with the same efficiency on both strains. On the other hand, the half lives of newly synthesized RNA as well as of functional beta-galactosidase mRNA are similar in both kind of strains. These two parameters, however, are significantly longer in both strains as compared to the original strain from which they were derived. Also, no difference in the differential induction of beta-galactosidase was observed between such strains. Thus, we have to conclude that either ribonuclease III does not play a significant role in the functioning and stability of newly synthesized mRNA, or that enough enzymatic activity was left, residual RNase III or some other enzyme to deal with double-stranded regions in the message.
Localization of a mutation affecting ribonuclease III activity (an enzyme specific for double-stranded ribonucleic acid) in Escherichia coli was attempted. By a series of matings and transduction experiments, the mutation rnc-105 was mapped near the nadB gene. In strains carrying this mutation, another mutation (ranA2074) was also found. Based on available data, their order on the E. coli chromosome appears to be tyrA, ranA, nadB, rnc, purI. Strains carrying either the ranA2074 or the rnc-105 mutation fail to grow at 45 C in enriched medium, whereas strains carrying only the rnc-105 mutation are defective in ribonuclease III activity. Strains carrying either of these mutations grow more slowly than corresponding wild-type strains in all media tested at all temperatures; the rnc-105 mutation reduces the growth rate more than the ranA2074 mutation. T4 and T7 bacteriophages form plaques with a lower efficiency on strains carrying the rnc-105 mutation than on other strains. Thus we suggest that ribonuclease III is beneficial for normal growth of E. Coli and that at higher temperatures it becomes indispensable.
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