Search PubMed⌕ Search

Biomedical subjects

R W West

Publications and source records attributed to R W West.

52 records · Page 3Linked to original sources
PubMed1979

Characterizing wild-type and mutant promoters of the tetracycline resistance gene in pBR313.

By employing a system of RNA polymerase binding and restriction endonuclease digestion, we demonstrate that the region in and around the Hind III site of pBR313 and pBR322 is the promoter for the tetracycline (Tc) resistance gene(s). Furthermore, it is shown that this region was transferred intact from pSC101 during the construction of the latter plasmids. The in vitro insertion of a few base pairs at the Hind III site produces a series of "down" promoter mutations in which the level of in vivo Tc resistance is reduced. Sequence analysis of the various promoter mutations revealed significant base pair rearrangements in the region between -40 and -12 of the promoter. While these base alterations do not appear to affect the firm binding of RNA polymerase, they do affect the ability of mutant promoters to initiate transcription. These observations suggest that the region from -40 to -12, previously designated as the "recognition region", is actually involved in the process of initiation of transcription.

Base Sequence↗
PubMed1979

Construction and characterization of E. coli promoter-probe plasmid vectors. I. Cloning of promoter-containing DNA fragments.

Derivatives of the Escherichia coli drug-resistance plasmid pBR316 have been constructed which act as molecular probes for promoter-containing DNA restriction fragments from various prokaryotic genomes. The plasmids, designated pBRH1 and pBRH3B, contain a unique EcoRI restriction site located within the promoter for the tetracycline resistance (Tcr) gene. This site was created by the insertion of a chemically synthesized octanucleotide, containing the EcoRI cleavage sequence, into the HindIII site of pBR316. Base-pair alterations within the Tc promoter produced by this insertion resulted in a substantial reduction (pBRH3B) or elimination (pBRH1) in ability of these plasmids to confer Tc resistance to the host strain. Cloning of EcoRI-cleaved foreign DNA fragments into the EcoRI site of these plasmids allows for the isolation of recombinant transformants with Tcr levels greater than that of the plasmid vector. Further characterization of these recombinant plasmids demonstrates that the Tcr phenotype is dependent upon the orientation of the inserted fragment, but not on the molecular weight. We have concluded that these fragments carry promoters which, in the proper orientation, allow for the transcription of the Tcr gene. The utility of these "promoter-probe" plasmids lies in the ability to select for promoter-containing DNA fragments by insertional activation of the Tcr gene.

Bacillus subtilis↗
PubMed1978

Subsynaptic plate perforations: changes with age and experience in the rat.

The relative frequency of appearance of discontinuities in the postsynaptic thickening, or perforations in the subsynaptic plate, increased with age and experience. Rats reared from weaning in complex or social environments had a significantly higher proportion of occipital cortical synapses with perforations than did rats reared in isolation. In addition, the relative frequency of these perforations more than tripled between 10 and 60 days of age. Shifts in the frequency of perforations can occur independently of changes in the size of synpases. This result suggests a new potential mechanism of synaptic plasticity.

Aging↗
PubMed1978

Single-mouse urine collection and pH monitoring system.

A glass cage with minimal surface area was designed and used to house mice for 24-hour urine collections. An experiment was performed with a radio-labeled compound excreted in the urine to assess the collection efficiency of the cage. In this experiment 74.2 +/- 6.5% of the excreted radioactivity was recovered in the urine, with 25.8 +/- 6.5% found adhering to the cage surfaces. When a flow-through pH electrode, meter, and recorder were attached, the system provided a continuous pH versus time urination record.

Animals↗
PubMed1977

Synaptic connections of the interplexiform cell in the retina of the cat.

Electron microscopy of Golgi-impregnated material and of well fixed, ultrathin serial sections has revealed the synaptic connections of interplexiform cells in cat retina. In the inner plexiform layer these cells are postsynaptic to amacrine cells and probably presynaptic to both bipolars and amacrines. In the outer plexiform layer they are presynaptic to rod and cone bipolar cells and also pre- and postsynaptic to other interplexiform cell dendrites. The interplexiform cell in cat retina appears to be concerned with feeding back information from the inner plexiform layer to the dendrites of bipolar cells in the outer plexiform layer.

Animals↗
PubMed1976

Light and electron microscopy of the ground squirrel retina: functional considerations.

Light and electron microscopy of Golgi-impregnated ground squirrel retinas have revealed a range of morphological subtypes of bipolar, amacrine, and ganglion cells. There are at least seven subtypes of bipolar cells. Those subtypes in which the somata were high (sclerad) in the inner nuclear layer (3 subtypes) had axon terminals low (vitread) in the inner plexiform layer, and those with somata low in the inner nuclear layer (4 subtypes) had axon terminals high in the inner plexiform layer. The bipolar subtypes with high axon terminals made flat contacts with receptor cells, whereas all but one of the bipolar subtypes with low axon terminals made ribbon-related contacts with receptor cells. There are at least five subtypes of amacrine cells. The two subtypes which the Golgi method revealed most frequently were a broad-field, unistratified neuron with a dendritic spread in excess of 1,000 mum and a narrow-field, diffuse neuron with a dendritic spread of about 30 mum. The broad-field, unistratified cell had the lowest proportion of amacrine vs. bipolar cell synaptic input of the amacrine subtypes (43%), whereas the narrow-field, diffuse cell had one of the greatest proportions of amacrine cell input (96%). There are at least 15 subtypes of ganglion cells. The proportion of synaptic inputs to these cells ranged from 21% to 100% amacrine cell synapses. An attempt has been made to relate this new knowledge of retinal circuitry to the physiological output of the ganglion cells.

Animals↗
PubMed1976

A re-examination of anatomical plasticity in the rat retina.

Previous investigators have reported an increase in numbers of amacrine synapses in the inner plexiform layer (IPL) of the rat retina following light deprivation, and an increase in amacrine along with a decrease in bipolar synapses following light damage. Since there are several points of disagreement between the published reports on this subject we undertook a more detailed study of the effects of light deprivation and light damage on the retina. Four groups of eight male albino rat pups (14 days old) were raised for eight weeks under different conditions: (1) unsutured, bright light reared (UB); (2) bilaterally lid-sutured, bright light reared (SB); (3) unsutured, low light reared (UL); and (4) bilaterally lid-sutured, dark reared (SD). The intensity of the light given the UL group was equated with that striking the corneas of the SB group. Light microscopy showed that the retinas of the SB as well as the UB groups had almost complete degeneration of the outer retinal layers, indicating that even low intensity light, when continuous, causes severe retinal damage. The SD group was thicker in many of the retinal layers compared to the UL (control) group. Electron microscopy revealed that there were no significant changes in the incidences of any type of synapse in the IPL following light deprivation or light damage when averaged over total depth. This is in contradiction to the reports of other investigators. However, when the IPL was analyzed by levels, the incidence of amacrine-ganglion synapses was signficantly greater (p less than 0.05) in groups UB and SD, but only in the outer third of the IPL. Thus, extensive postnatal plasticity of IPL synapses in the rat retina did not occur under our experimental conditions. We found, at best, only limited effects which were confined to the amacrine-ganglion synapses.

Animals↗
PubMed1975

Anatomical evidence for cone and rod-like receptors in the gray squirrel, ground squirrel, and prairie dog retinas.

In the gray squirrel (Sciurus carolinensis), the prairie dog (Cynomys ludovicianus), and the Mexican and 13-line ground squirrels (Citellus mexicanus and C. tridecemlineatus) there exist two distinct classes of photo-receptors that have cone-like and rod-like anatomical features respectively. These two receptor classes were previously known to exist in the gray squirrel, but only the cone-like (C) receptor had been observed in the other species. We have now found small numbers of rod-like (R) receptors in the other species as well. R-receptors comprise about 40% of the receptors in the gray squirrel, 10% of the receptors in the prairie dog, and 4-5% of the receptors in the two species of ground squirrel. This paper describes certain light and electron microscopic features of these two receptor classes including their synaptic connections with second-order cells and with each other. We find that the C-receptor has a morphology and synaptic organization characteristic of other mammalian cones. However, the R-receptor differs from other mammalian rods in certain morphological respects, and its synaptic organization has both cone and rod characteristics as well as some unusual features.

Animals↗
PubMed1972

Synapses onto different morphological types of retinal ganglion cells.

The percentage of bipolar and amacrine synapses onto ganglion cell dendrites of the ground squirrel has been determined by electron microscopy of cells impregnated by the Golgi method. One group of ganglion cells has mainly amacrine input (approximately 97 percent); the other group has an approximately equal bipolar and amacrine input. Morphologically distinct types of ganglion cells usually have a consistent synaptic input, but exceptions may exist.

Animals↗