Flagellar hook and basal complex of Caulobacter crescentus.

Intact bacterial flagella possessing a membrane-free hook and basal complex were purified from Caulobacter crescentus CB15, as well as from mutants which synthesize incomplete flagella. The basal body consisted of five rings mounted on a rod. Two rings were in the hook-proximal upper set, and three rings (two narrow and one wide) were in the lower set. The diameters of the two upper rings differed, being 32 and 21 nm, respectively. The lower rings were all approximately 21 nm in diameter, although they varied significantly in width. During the normal course of the C. crescentus cell cycle, the polar flagellum with hook and rod was shed into the culture medium without the basal rings. Similarly, hooks with attached rods were shed from nonflagellate mutants, and these structures also lacked the basal rings. The hook structure was purified from nonflagellated mutants and found to be composed of a 70,000-molecular-weight protein component.     

Lipid and lipopolysaccharide composition of Escherichia coli surface-altered mutants selected for resistance to levallorphan, tetracaine, and polymyxin.

Certain mutants of Escherichia coli with an altered permeability barrier have an essentially normal lipopolysaccharide, fatty acid, and phospholipid content, with a slight increase in the membrane protein:lipid ratio. The phospholipid metabolism of the lev and tec strains shows an abnormal response to growth in the selective agents levallorphan and tetracaine, respectively.     

Minimal requirements in defined media for improved growth of some radio-resistant pink tetracocci.

Defined media permitting extensive growth of representative pink radio-resistant tetracocci (Micrococcus radiodurans, Micrococcus roseus, and Micrococcus radiophilus) and two controls (an ultraviolet-sensitive mutant of M. radiodurans and Micrococcus luteus) are described. Availability of Fe (especially Fe3+) proved essential for good growth, as evidenced by (i) favorable effects of hydroxamic acids, e.g., salicylhydroxamic acid, and (ii) the growth promotion by hemin when joined with elevated concentrations of Fe. Cobalamin (B12) and methionine were interchangeable as an absolute requirement for methionine not affected by B12. M. luteus required neither. Pink radio-resistant micrococci may form a coherent group. Some divergences among them might be attributable to the method for isolating them, which for ordinary bacteria would be mutagenic to the point of total lethality. The ecology of these tetracocci vis-à-vis other pink-red radio-resistant organisms is discussed in relation to a question: can these bacteria be isolated without dependence on radiation as the cardinal selective factor?     

Function of S-adenosylmethionine in germinating yeast ascospores.

Germination and outgrowth of ascospores of Saccharomyces cerevisiae 4579 require both methionine and adenine, whereas leucine is only required for outgrowth. The methionine requirement may be satisfied by S-adenosylmethionine, but this sulfonium compound will not substitute for adenine. Between 30 and 70 min of protein synthesis is initially required for the completion of germination in strain 4579. The inhibition of S-adenosylmethionine synthetase by trifluoromethionine prevents both germination and protein synthesis. During the initial stages of germination, the S-adenosylmethionine synthetase, S-adenosylmethionine decarboxylase, and transfer ribonucleic acid methyltransferases increased significantly, indicating that polyamines and/or the methylation of transfer ribonucleic acid are required for the initiation of germination.     

Tn402: a new transposable element determining trimethoprim resistance that inserts in bacteriophage lambda.

We have found that the trimethoprim resistance determinant of the IncP plasmid R751 (Jacob et al., 1977; Jobanputra and Datta, 1974) transposes to bacteriophage lambda. We call this transposable element Tn402.     

An enzyme mechanism language for the mathematical modeling of metabolic pathways

MOTIVATION: As a first step toward the elucidation of the systems biology of complex biological systems, it was our goal to mathematically model common enzyme catalytic and regulatory mechanisms that repeatedly appear in biological processes such as signal transduction and metabolic pathways. RESULTS: We describe kMech, a Cellerator language extension that describes a suite of enzyme mechanisms. Each enzyme mechanism is parsed by kMech into a set of fundamental association-dissociation reactions that are translated by Cellerator into ordinary differential equations that are numerically solved by Mathematica. In addition, we present methods that use commonly available kinetic measurements to estimate rate constants required to solve these differential equations.     

Phosphoinositide lipid second messengers: new paradigms for calcium channel modulation

Neuronal Ca2+ channels are key transducers coupling excitability to cellular function. As such, they are tightly regulated by multiple G protein-signaling pathways that finely tune their activity. In addition to fast, direct G(beta)gamma modulation of Ca2+ channels, a slower Galpha(q/11)-mediated mechanism has remained enigmatic despite intensive study. Recent work suggests that membrane phosphoinositides are crucial determinants of Ca2+ channel activity. Here, we discuss their role in Ca2+ channel modulation and the leading theories that seek to elucidate the underlying molecular details of the so-called "mysterious" G(q/11)-mediated signal.     

The bacterial nucleoid: a highly organized and dynamic structure

Recent advances in bacterial cell biology have revealed unanticipated structural and functional complexity, reminiscent of eukaryotic cells. Particular progress has been made in understanding the structure, replication, and segregation of the bacterial chromosome. It emerged that multiple mechanisms cooperate to establish a dynamic assembly of supercoiled domains, which are stacked in consecutive order to adopt a defined higher-level organization. The position of genetic loci on the chromosome is thereby linearly correlated with their position in the cell. SMC complexes and histone-like proteins continuously remodel the nucleoid to reconcile chromatin compaction with DNA replication and gene regulation. Moreover, active transport processes ensure the efficient segregation of sister chromosomes and the faithful restoration of nucleoid organization while DNA replication and condensation are in progress.