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Biomedical subjects

A Zaritsky

Publications and source records attributed to A Zaritsky.

126 records · Page 7Linked to original sources
PubMed1978

Chromosome replication rate and cell shape in Escherichia coli: lack of coupling.

The dimensions of Rep- cells of Escherichia coli K-12 were measured and compared with those of their Rep+ isogenic cells (both Thy-), Rep- cells cultivated identically were longer (but not wider), even though both strains were wider when the rate of chromosome replication was slowed down by lowering the thymine concentration supplied. This eliminates the possibility that cell shape is determined by this rate. Simulating Thy+ phenotype by adding deoxyguanosine resulted in shorter Rep- cells when growth was faster. This excludes a simple relationship between cell elongation and growth rate, but is consistent with a linear proportionality between the rate of surface synthesis and growth. Thymine limitation of fast-growing Thy- E. coli K-12 cells is shown to result in loss of their uniform shape and production of bizarre morphologies, apparently due to imbalanced synthesis of wall components.

Chromosomes, Bacterial↗
PubMed1975

Rate stimulation of deoxyribonucleic acid synthesis after inhibition.

The degree to which the rate of deoxyribonucleic acid synthesis in thy- cultures of Escherichia coli is stimulated after a period of thymine starvation is shown to be a function of the concentration of thymine present as well as of the culture doubling time. Inhibition of deoxyribonucleic acid synthesis by nalidixic acid yields comparable results. Periods of thymine starvation exceeding one doubling time appear to cause an irreversible inactivation of a fraction of the replication forks in the culture.

Carbon Radioisotopes↗
PubMed1973

Changes in cell size and shape associated with changes in the replication time of the chromosome of Escherichia coli.

Average cell mass is shown to be inversely related to the concentration of thymine in the growth medium of a thy(-) strain of Escherichia coli. The kinetics of the transition from one steady-state average cell mass to another was followed in an attempt to determine the relationship between the chromosome replication time and the time between completion of a round of chromosome replication and the subsequent cell division. Differences in average cell mass are shown to be associated with similar differences in average cell volume. Changes in volume associated with changes in thymine concentration are shown to be due primarily to differences in the width of cells. It is proposed that extension in length of the cell envelope occurs at a linear rate which is proportional to the growth rate and which doubles at the time of termination of rounds of replication. Changes in volume not associated with a change in growth rate are therefore accommodated by a change in cell width. Conditions are described under which average cell mass can continue to increase in successive generations and no steady-state average cell mass is achieved.

Carbon Isotopes↗
PubMedDate not supplied

Effects of temperature inactivation of penicillin-binding protein 2 on envelope growth in Escherichia coli.

The transition from rod-shaped to spheroidal cells was studied in a temperature-sensitive strain (SP45) of Escherichia coli K12, carrying a mutation (pbpA) in the gene coding for penicillin-binding protein 2 (PBP-2). This transition imposed by the restrictive temperature was associated with reduction of peptidoglycan/surface area and of cellular osmotic stability. Addition of nalidixic acid (20 micrograms/ml) at the temperature shift from 30 to 42 degrees C resulted in lysis of some cells and appearance of spheroidal bulges along the cylinders in other cells, consistent with the hypothesis of envelope weakening due to inactivation of PBP-2.

Acyltransferases↗
PubMedDate not supplied

Visualizing multiple constrictions in spheroidal Escherichia coli cells.

An Escherichia coli cell grows by elongation and divides in a perpendicular plane. Alternating planes of successive divisions in three dimensions can only be ascertained when multiple constrictions exist simultaneously in large, spheroidal cells (with extended constriction process), if the division signals are enhanced. Large, spheroidal cells are obtained by a brief mecillinam treatment, and more frequent divisions are achieved by manipulating the rate of chromosome replication without affecting cell mass growth rate. Such a procedure has recently been performed by thymine-limitation of E. coli K12 strain CR34 (Zaritsky et al., Microbiology 145 (1999), 1052-1022). Enhancing the replication rate in cells with multi-forked replicating chromosomes (by addition of deoxyguanosine) shortens the intervals between successive terminations and thus triggers divisions more frequently. Monoclonal antibodies against FtsZ were used to visualize the rings of secondary constrictions, but apparent shortage of FtsZ to complete rings over wide cells allowed assembly of arcs only. The arcs observed were not parallel nor perpendicular; the tilted constriction planes are consistent with our 3-D 'nucleoid segregation'model for division under conditions which relieve the cylindrical constraint for nucleoid segregation by the bacillari peptidoglycan sacculus (Woldringh et al. , J. Bacteriol. 176 (1994) 6030-6038). The shortage in FtsZ may explain the longer time required to complete the division process in wide cells with long circumferences, observed during thymine step-up. Overexpression of fusion protein FtsZ-GFP on a multi-copy plasmid should circumvent the shortage.

Bacterial Proteins↗