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C S Potter

Publications and source records attributed to C S Potter.

18 recordsLinked to original sources
PubMed2001

Automated identification of filaments in cryoelectron microscopy images.

Since the foundation for the three-dimensional image reconstruction of helical objects from electron micrographs was laid more than 30 years ago, there have been sustained developments in specimen preparation, data acquisition, image analysis, and interpretation of results. However, the boxing of filaments in large numbers of images--one of the critical steps toward the reconstruction at high resolution--is still constrained by manual processing even though interactive interfaces have been built to aid the tedious and sometimes inaccurate boxing process. This article describes an accurate approach for automated detection of filamentous structures in low-contrast images acquired in defocus pairs using cryoelectron microscopy. The performance of the approach has been evaluated across various magnifications and at a series of defocus values using tobacco mosaic virus (TMV) preserved in vitreous ice as a test specimen. By integrating the proposed approach into our automated data acquisition and reconstruction system, we are now able to generate a three-dimensional map of TMV to approximately 10-A resolution within 24 h of inserting the specimen grid into the microscope.

Algorithms↗
PubMed2000

Leginon: an automated system for acquisition of images from vitreous ice specimens.

We have developed a system to automatically acquire cryo-electron micrographs. The system is designed to emulate all of the decisions and actions of a highly trained microscopist in collecting data from a vitreous ice specimen. These include identifying suitable areas of vitreous ice at low magnification, determining the presence and location of specimen on the grid, automatically adjusting imaging parameters (focus, astigmatism) under low-dose conditions, and acquiring images at high magnification to either film or a digital camera. This system is responsible for every aspect of image acquisition and can run unattended, other than requiring periodic refilling of the cryogens, for over 24 h. The system has been tested out on a variety of specimens that represent typical challenges in the field of cryo-electron microscopy. The results show that the overall performance of the system is equivalent to that of an experienced microscopist.

Computer Graphics↗
PubMed1999

Improving the positional accuracy of the goniometer on the Philips CM series TEM.

We have developed a method to improve the accuracy for absolute relocation of a target specimen using the goniometer on a Philips transmission electron microscope. We have achieved this by characterizing the performance of the Philips compustage, modeling its behavior, and using this model to calculate the goniometer movements required for accurate target relocation. This resulted in a 10-fold improvement in the positioning accuracy of the goniometer.

Algorithms↗
PubMed1999

Leginon: a system for fully automated acquisition of 1000 electron micrographs a day.

We have developed a system to automatically acquire large numbers of acceptable quality images from specimens of negatively stained catalase, a biological protein which forms crystals. In this paper we will describe the details of the system architecture and analyze the performance of the system as compared to a human operator. The ultimate goal of the system if to automate the process of acquiring cryo-electron micrographs.

Automation↗
PubMed1987

Hepatic disposition and biliary excretion of bilirubin and bilirubin glucuronides in intact rats. Differential processing of pigments derived from intra- and extrahepatic sources.

Mechanisms for transport of bilirubin and its conjugates in hepatocytes have not been defined. We investigated the hepatic processing of bilirubin glucuronides and their precursors, and characterized the disposition of bile pigments arising from intraversus extrahepatic sources. Tracer doses of purified radiolabeled biliverdin, bilirubin, bilirubin monoglucuronide (BMG) or diglucuronide (BDG) were administered intravenously to intact normal or jaundiced homozygous Gunn rats. Rapid sequential analysis of radiolabeled BMG and BDG in bile revealed comparable excretion patterns following biliverdin and bilirubin injection, with BDG as the major pigment. Biliary excretion of radiolabeled conjugates from injected BMG was more rapid, with BMG predominating. Excretion of injected BDG in normal rats and BMG or BDG in Gunn rats was virtually identical to that of unaltered BMG in normal rats. Model independent analysis by deconvolution provided objective comparison of the disposition of radiolabeled pigments from the different sources. These findings indicate that bilirubin glucuronides formed in the liver from endogenous (hepatic) and exogenous (extrahepatic) sources of bilirubin follow a similar excretory pathway. BMG formed endogenously is converted preferentially to BDG, whereas circulating BMG is excreted predominantly unchanged. Exogenous conjugated bilirubins are excreted more rapidly than those generated intrahepatically, by a transcellular pathway that is largely independent of the conjugation system.

Animals↗
PubMed1973

Defects in prodigiosin formation by L-forms of Serratia marcescens.

An L-form of Serratia marcescens has previously been shown incapable of producing the red pigment, prodigiosin, characteristic of the parent bacteria. Mutants of S. marcesens, unable to form one or the other of the two prodigiosin precursors, 4-methoxy-2,2'-bipyrrole-5-carboxaldehyde or 2-methyl-3-n-amylpyrrole, were used to test the nature of the L-form defect. The L-forms failed to form sufficient amounts of either precursor to be detected by the appropriate mutant, and, when furnished the precursors, failed to couple them to form prodigiosin.

Cell Count↗
PubMed1971

L-forms of Pseudomonas aeruginosa.

L-forms of a strain of Pseudomonas aeruginosa were produced by serial subculture of the bacterial form on agar medium containing sucrose as an osmotic stabilizer and carbenicillin. L-forms eventually became stable, i.e., would not revert in the absence of antibiotic, and were adapted to grow well in broth with the osmotic stabilizer. Gross morphology and light microscopic colony morphology were typical of an L-form. L-form cells were approximately spherical and bounded in part by a plasma membrane; they lacked the triple-layer cell wall structure and coarse, electron-dense nucleoidal granules of the parent bacterial form. The L-form, but not the bacterial form, contained cores, organelles previously reported only in group D streptococci. Antibiotic disc-sensitivity studies showed the stable L-form to be as sensitive as, or more sensitive than, the bacterial form to most antibiotics. Exceptions were polymyxin B, colimycin sulfate, and gentamicin, which were more active against the bacterial form. The remainder of the aminoglycosides and cell wall-active antibiotics showed no inhibition of either form. The L-form was more susceptible to cidal activity of normal human serum than the parent form. The L-form exhibited fewer biochemical activities than the parent bacteria or bacterial forms derived by reversion at a time when the L-form was still unstable. L-form colonies appeared colorless, and chemical analysis demonstrated that, if the L-form produces pigment at all, which was not demonstrated, it could not have been more than 3.6% of that produced by the bacterial form.

Anti-Bacterial Agents↗
PubMed1971

Differential action of a streptococcal bacteriocin on mycoplasmas and microbial L-forms.

Bacteriocin activity of Streptococcus faecalis var. zymogenes was tested against a variety of bacteria, L-forms, and mycoplasmas. Both a partially purified liquid preparation and a colony overlay technique were used. Other S. faecalis strains were the only bacteria whose growth was inhibited. The liquid preparation inhibited growth of all but three of the tested L-forms (whether derived from gram-positive or gram-negative bacteria), and two of these exceptional organisms were inhibited when the colony overlay technique was employed. On the other hand, the L-form of Streptobacillus moniliformis and all 33 tested mycoplasmas grew readily in the presence of the bacteriocin when either method was employed. It is suggested that the presence of cholesterol in the Streptobacillus and mycoplasmal membranes, unique in this regard among procaryotic cells, may be responsible for the differential pattern of growth inhibition.

Bacteriocins↗
PubMed1968

Penicillin: effect on sodium and potassium transport in bacterial and protoplast forms of Sterptococcus faecalis.

Streptococcus faecalis, incubated in osmotically stabiliz medium in the presence of 1000 units of penicillin per milliliter, accumulated rather than extruded sodium; they accumulated much less potassium than control cells did. These changes were not due to binding of sodium by cell-wall fragments of cells treated with penicillin. Because penicillin had no effect on cation concentrations in stable protoplasts and nongrowing bacterial cells, this effect appeared to be related to the production of the penicillin-induced lesions of the cell wall.

Biological Transport, Active↗
PubMedDate not supplied

JavaScope: A Web-based TEM control interface.

JavaScope is a Web-based java applet that implements an "exploration/browser" tool for operating a Philips CM200 transmission electron microscope and viewing digital images remotely. The primary use of the application is as a collaborative tool for remote consultations.

Image Processing, Computer-Assisted↗
PubMedDate not supplied

Automated image acquisition for single-particle reconstruction using p97 as the biological sample.

We have used Leginon, a fully automatic system capable of acquiring cryo-electron micrographs, to collect data of single particles, specifically of the AAA ATPase p97. The images were acquired under low-dose conditions and required no operator intervention other than the initial setup and periodic refilling of the cold-stage dewar. Each image was acquired at two different defocus values. Two-dimensional projection maps of p97 were calculated from these data and compared to results previously obtained using the conventional manual data collection methods to film. The results demonstrate that Leginon performs as well as an experienced microscopist for the acquisition of single-particle data. The general advantages of automation are discussed.

Adenosine Triphosphatases↗