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T Powers

Publications and source records attributed to T Powers.

54 records · Page 3Linked to original sources
PubMed1989

Defining the structural requirements for a helix in 23 S ribosomal RNA that confers erythromycin resistance.

The helix spanning nucleotides 1198 to 1247 (helix 1200-1250) in Escherichia coli 23 S ribosomal RNA (rRNA) is functionally important in protein synthesis, and deletions in this region confer erythromycin resistance. In order to define the structural requirements for resistance, we have dissected this region using in vitro mutagenesis. Erythromycin resistance is established after a minimal deletion of three bases, CAU1231 or AUG1232. The maximum deletion observed to confer resistance is 25 bases. The level of erythromycin resistance conferred by intermediate sized deletions is variable and some deletion mutants show a sensitive phenotype. Deletions that extend into the base-pairing between GCC1208 and GGU1240 result in non-functional 23 S RNAs, which consequently do not confer resistance. A number of phylogenetically conserved nucleotides have been shown to be non-essential for 23 S RNA function. However, removal of either these or non-conserved nucleotides from helix 1200-1250 measurably reduces the efficiency of 23 S RNA in forming functional ribosomes. We have used chemical probing and a modified primer extension method to investigate erythromycin binding to wild-type and resistant ribosomes with a 12-base deletion in 23 S RNA. Erythromycin interacts as strongly with mutant 23 S RNA as with wild-type 23 S RNA. Deletions in the 1200-1250 helix do not therefore confer resistance by reducing erythromycin binding, but by suppressing the effects of the drug at the level of its mechanism of action.

Base Sequence↗
PubMed1989

RNA-protein interactions in 30S ribosomal subunits: folding and function of 16S rRNA.

Chemical probing methods have been used to "footprint" 16S ribosomal RNA (rRNA) at each step during the in vitro assembly of twenty 30S subunit ribosomal proteins. These experiments yield information about the location of each protein relative to the structure of 16S rRNA and provide the basis for derivation of a detailed model for the three-dimensional folding of 16S rRNA. Several lines of evidence suggest that protein-dependent conformational changes in 16S rRNA play an important part in the cooperativity of ribosome assembly and in fine-tuning of the conformation and dynamics of 16S rRNA in the 30S subunit.

Base Sequence↗
PubMed1988

Interaction of ribosomal proteins S5, S6, S11, S12, S18 and S21 with 16 S rRNA.

We have examined the effects of assembly of ribosomal proteins S5, S6, S11, S12, S18 and S21 on the reactivities of residues in 16 S rRNA towards chemical probes. The results show that S6, S18 and S11 interact with the 690-720 and 790 loop regions of 16 S rRNA in a highly co-operative manner, that is consistent with the previously defined assembly map relationships among these proteins. The results also indicate that these proteins, one of which (S18) has previously been implicated as a component of the ribosomal P-site, interact with residues near some of the recently defined P-site (class II tRNA protection) nucleotides in 16 S rRNA. In addition, assembly of protein S12 has been found to result in the protection of residues in both the 530 stem/loop and the 900 stem regions; the latter group is closely juxtaposed to a segment of 16 S rRNA recently shown to be protected from chemical probes by streptomycin. Interestingly, both S5 and S12 appear to protect, to differing degrees, a well-defined set of residues in the 900 stem/loop and 5'-terminal regions. These observations are discussed in terms of the effects of S5 and S12 on streptomycin binding, and in terms of the class III tRNA protection found in the 900 stem of 16 S rRNA. Altogether these results show that many of the small subunit proteins, which have previously been shown to be functionally important, appear to be associated with functionally implicated segments of 16 S rRNA.

Autoradiography↗
PubMed1988

Probing the assembly of the 3' major domain of 16 S rRNA. Interactions involving ribosomal proteins S2, S3, S10, S13 and S14.

We have used rapid probing methods to follow the changes in reactivity of residues in 16 S rRNA to chemical and enzymatic probes as ribosomal proteins S2, S3, S10, S13 and S14 are assembled into 30 S subunits. Effects observed are confined to the 3' major domain of the RNA and comprise three general classes. (1) Monospecific effects, which are attributable to a single protein. Proteins S13 and S14 each affect the reactivities of different residues which are adjacent to regions previously found protected by S19. S10 effects are located in two separate regions of the domain, the 1120/1150 stem and the 1280 loop; both of these regions are near nucleotides previously found protected by S9. Both S2 and S3 protect different nucleotides between positions 1070 and 1112. In addition, S2 protects residues in the 1160/1170 stem-loop. (2) Co-operative effects, which include residues dependent on the simultaneous presence of both proteins S2 and S3 for their reactivities to appear similar to those observed in native 30 S subunits. (3) Polyspecific effects, where proteins S3 and S2 independently afford the same protection and enhancement pattern in three distal regions of the domain: the 960 stem-loop, the 1050/1200 stem and in the upper part of the domain (nucleotides 1070 to 1190). Proteins S14 and S10 also weakly affect the reactivities of several residues in these regions. We believe that several of the protected residues of the first class are likely sites for protein-RNA contact while the third class is indicative of conformational rearrangement in the RNA during assembly. These results, in combination with the results from our previous study of proteins S7, S9 and S19, are discussed in terms of the assembly, topography and involvement in ribosomal function of the 3' major domain.

Autoradiography↗
PubMed1988

Probing the assembly of the 3' major domain of 16 S ribosomal RNA. Quaternary interactions involving ribosomal proteins S7, S9 and S19.

We have studied the effect of assembly of ribosomal proteins S7, S9 and S19 on the accessibility and conformation of nucleotides in 16 S ribosomal RNA. Complexes formed between 16 S rRNA and S7, S7 + S9, S7 + S19 or S7 + S9 + S19 were subjected to a combination of chemical and enzymatic probes, whose sites of attack in 16 S rRNA were identified by primer extension. The results of this study show that: (1) Protein S7 affects the reactivity of an extensive region in the lower half of the 3' major domain. Inclusion of proteins S9 or S19 with S7 has generally little additional effect on S7-specific protection of the RNA. Clusters of nucleotides that are protected by protein S7 are localized in the 935-945 region, the 950/1230 stem, the 1250/1285 internal loop, and the 1350/1370 stem. (2) Addition of protein S9 in the presence of S7 causes several additional effects principally in two structurally distal regions. We observe strong S9-dependent protection of positions 1278 to 1283, and of several positions in the 1125/1145 internal loop. These findings suggest that interaction of protein S9 with 16 S rRNA results in a structure in which the 1125/1145 and 1280 regions are proximal to each other. (3) Most of the strong S19-dependent effects are clustered in the 950-1050 and 1210-1230 regions, which are joined by base-pairing in the 16 S rRNA secondary structure. The highly conserved 960-975 stemp-loop, which has been implicated in tRNA binding, appears to be destabilized in the presence of S19. (4) Protein S7 causes enhanced reactivity at several sites that become protected upon addition of S9 or S19. This suggests that S7-induced conformational changes in 16 S rRNA play a role in the co-operativity of assembly of the 3' major domain.

Aldehydes↗
PubMed1985

Unicompartmental and bicompartmental arthroplasty of the knee with a finned metal tibial-plateau implant.

We followed a series of ten patients (ten knees) who had a unicompartmental and twenty patients (twenty-two knees) who had a bicompartmental arthroplasty of the knee, in which a finned metal tibial-plateau implant had been used, for two to fourteen years (average, five years) postoperatively. According to the modified criteria of MacIntosh and Hunter, thirty knees (94 per cent) had a good result and two (6 per cent), a fair result. There were two complications: one intraoperative and one postoperative fracture of the tibial plateau. One patient with rheumatoid arthritis required a revision to a total knee arthroplasty at six months because of rapid progression of disease in the contralateral, untreated compartment. Our results suggest that with the proper indications this arthroplasty has a place in reconstructive surgery of the arthritic knee joint.

Adult↗
PubMedDate not supplied

Prospective randomized evaluation of two regimens for converting from continuous to intermittent feedings in patients with feeding gastrostomies.

Forty enterally fed male patients were randomized to one of two regimens designed to determine the better means of converting them from continuous to intermittent enteral feedings. All patients received a nutritionally complete iso-osmolal 1 kcal/cc formula containing 6 g of nitrogen/L beginning on the second postgastrostomy day. Half of the patients (20) were randomized to a discontinuous regimen abruptly changing from continuous to gradually increasing intermittent feedings until reaching their nutritional goals. Intravenous fluids were given to maintain normal fluid balance. The other 20 patients were randomized to an overlapping regimen, receiving continuous feedings at a decreasing rate while intermittent feedings were progressively increased. Intravenous fluids were used during the first three stages only. There were no significant differences (p less than 0.05) in major diagnosis, type of gastrostomy, age, weight, height, admission or discharge serum albumin concentration, calculated basal energy expenditure (BEE), or nutrient goals (1.5 X BEE, 1.5 g of protein/kg per day).(ABSTRACT TRUNCATED AT 250 WORDS)

Diarrhea↗
PubMedDate not supplied

Experimental hyperextension supracondylar fractures in monkeys.

Discarded monkey autopsy specimens were used to investigate the mechanism of supracondylar hyperextension fracture. As the fracture progressed from mild angulation to complete lateral or medial displacement, the anterior periosteum first was detached from the bone and then stripped distally before tearing over the edge of the proximal fragment. Stability or reduction by acute elbow flexion and forearm pronation, owing to compressive forces, was transmitted through the elbow joint on the medial side of the fracture, and stability was not significantly influenced by a bridging periosteal hinge or forearm musculature. Forearm supination and elbow flexion of less than 90 degrees resulted in less stability. The influence of acute elbow flexion and forearm pronation was diminished when the fracture was distracted by traction. Interposition of the anterior periosteum in displacement fractures prevented anatomic reduction.

Age Factors↗
PubMedDate not supplied

Analysis of the practice of nutrition support pharmacy specialists.

In 1988 the Board of Pharmaceutical Specialities (BPS) recognized nutrition support pharmacy practice (NSPP) as one of four specialty areas in pharmacy. The BPS appointed a specialty council to develop and manage the process for board certification of qualified specialists. One step was to identify and validate activities performed by the specialists. This was accomplished by conducting a study that delineated the role of these practitioners and also provided information for developing a blueprint for a certification examination. The results revealed the types of practice settings, education, and training for specialists, and the distribution of professional time devoted to nutrition support activities.

Certification↗