Fine structure observed in 50S ribosomal subunits of Bacillus subtilis.
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Bacillus subtilis↗
Biomedical subjects
N Nanninga
Publications and source records attributed to N Nanninga.
On the role of the high molecular weight penicillin-binding proteins in the cell cycle of Escherichia coli.
Blocking of penicillin-binding proteins (PBP) 2 or 3 of Escherichia coli by specific antibiotics led to inhibition of peptidoglycan synthesis measured as rate of 3H-Dap incorporation. The inhibition was ca 60% by mecillinam (blocking PBP2) and ca 35% by cephalexin or furazlocillin (both specific for PBP3). PBP3 could be inhibited primarily during constriction, whereas the inhibition of PBP2 was observed throughout the cell cycle. The ratio of PBP2 and 3 activities appeared to be correlated with cell shape, i.e. in long rods, inhibition of peptidoglycan synthesis by mecillinam was stronger than in short rods. Inhibition studies with the PBP1A/1B-specific antibiotic cefsulodin showed that, with a delay of approximately 1/2 mass-doubling time, peptidoglycan synthesis was inhibited completely with concomitant lysis. The cefsulodin-induced lysis was independent of the stage of the cell cycle. It was suggested that PBP1A/1B do not have a specific function in either elongation or constriction. Rather, they seem to have a general activity on the basis of which the other synthesizing PBP perform their special tasks. This interpretation is formulated as a "primer model of peptidoglycan synthesis".
Anti-Bacterial Agents↗
Escherichia coli contains a DNA replication compartment in the cell center.
The active replication forks of E. coli B/r K cells growing with a doubling time of 210 min have been pulse-labeled with [(3)H] thymidine for 10 min. By electron-microscopic autoradiography the silver grains have been localized in the various length classes. From the known pattern of the DNA replication period in the cell cycle at slow growth and from the average position of grains per length class it was deduced that DNA replication starts in the cell center and that it remains there for a substantial part of the DNA replication period. This suggests the occurrence of a centrally located DNA replication compartment.
Autoradiography↗
Cellular localization of oriC during the cell cycle of Escherichia coli as analyzed by fluorescent in situ hybridization.
The origin of replication of Escherichia coli, oriC, has been labeled by fluorescent in situ hybridization (FISH). The E. coli K12 strain was grown under steady state conditions with a doubling time of 79 min at 28 degrees C. Under these growth conditions DNA replication starts in the previous cell cycle at -33 min. At birth cells possess two origins which are visible as two separated foci in fully labeled cells. The number of foci increased with cell length. The distance of foci from the nearest cell pole has been measured in various length classes. The data suggest: i) that the two most outwardly located foci keep a constant distance to the cell pole and they therefore move apart gradually in line with cell elongation; and ii) that at the initiation of DNA replication the labeled origins occur near the center of prospective daughter cells.
Cell Cycle↗
Stimulation and inhibition of cell division in synchronized Escherichia coli.
Escherichia coli was synchronized by centrifugal elutriation. When grown in a Tris-based medium, addition of EDTA resulted in division about 20 min earlier (division of control at t = 75 min). EDTA addition caused a change in cell shape, with cells becoming narrower and longer, whereas the surface area to volume ratio increased. Irradiation with UV inhibited not only division and constriction, but also the increase in DAP incorporation found in dividing control cells. Possibly, division requires the construction of new polar caps, whereas premature division might involve remodeling of existing murein. In both cases, cell shape is presumed to be a relevant factor for division.
Cell Division↗
Three-dimensional chromatin distribution in neuroblastoma nuclei shown by confocal scanning laser microscopy.
The relationship between cell shape and function has long been of interest. However, although the behaviour of the cytoskeleton during the cell cycle has been studied extensively variations in the shape and three-dimensional substructure of the nucleus are less well documented. The spatial distribution of chromatin has previously been studied by a mathematical analysis of the optical densities of stained nuclei, allowing an indirect derivation of the three-dimensional distribution of chromatin. More direct information on chromatin organization can be obtained from electron-microscopic serial sections, although this is very laborious. Using an iterative deconvolution algorithm, Agard and Sedat achieved a degree of optical sectioning in conventional fluorescence microscopy and reconstructed the three-dimensional arrangement of polytene chromosomes. We report here on the three-dimensional structure of cultured mammalian cells as visualized by confocal scanning laser microscopy (CSLM). The exceptionally short depth of field of this imaging technique provides direct optical sectioning which, together with its higher resolution, makes CSLM extremely useful for studying the three-dimensional morphology of biological structures.
Anaphase↗