Despite being perceived as relatively simple organisms, many bacteria exhibit an impressive degree of subcellular organization. In Caulobacter crescentus, the evolutionarily conserved polar organizing protein PopZ facilitates cytoplasmic organization by recruiting chromosome centromeres and regulatory proteins to the cell poles. Here, we characterize the localization and function of PopZ in Agr...

We demonstrate that successive cleavage events involving regulated intramembrane proteolysis (Rip) occur as a function of time during the Caulobacter cell cycle. The proteolytic substrate PodJ(L) is a polar factor that recruits proteins required for polar organelle biogenesis to the correct cell pole at a defined time in the cell cycle. We have identified a periplasmic protease (PerP) that init...

Chromosome segregation in most animal cells is brought about through two events: the movement of the chromosomes to the poles (anaphase A) and the movement of the poles away from each other (anaphase B). Essential to an understanding of the mechanism of mitosis is information on the relative movements of components of the spindle and identification of sites of subunit loss from shortening micro...

Serial sections of mitotic spindles of the marine cryptophycean alga, Cryptomonas, were analysed to determine what types of microtubules they contained and which of these microtubules came close enough to each other (50 nm or less) for the commonly described crossbridging to be possible. Interpolar microtubules were rare (less than or equal to 1%) but from prometaphase through anaphase there wa...

Recent evidence suggests that cells employ functionally asymmetric partitioning schemes in division to cope with aging. We explore various schemes in silico, with a stochastic model of Escherichia coli that includes gene expression, non-functional proteins generation, aggregation and polar retention, and molecule partitioning in division. The model is implemented in SGNS2, which allows stochast...

Polar pili biogenesis in Caulobacter involves the asymmetric localization of the CpaE and CpaC components of the pili-specific secretion apparatus to one pole of the predivisional cell followed by the biosynthesis of the pili filaments in the daughter swarmer cell. The histidine kinase signaling protein, PleC, that controls the temporal accumulation of the PilA pilin subunit is asymmetrically l...

Each cell division in Caulobacter crescentus is asymmetric, yielding a swarmer cell with several polar pili and a non-piliated stalked cell. To identify factors contributing to the asymmetric biogenesis of polar pili, cytological studies of pilus assembly components were performed. We show here that the CpaC protein, which is thought to form the outer membrane pilus secretion channel, and its a...

Although lightning has been seen on other planets, including Jupiter, polar lightning has been known only on Earth. Optical observations from the New Horizons spacecraft have identified lightning at high latitudes above Jupiter up to 80 degrees N and 74 degrees S. Lightning rates and optical powers were similar at each pole, and the mean optical flux is comparable to that at nonpolar latitudes,...

T mitotic spindle is an impressive cellular machine, responsible for distributing each set of the duplicated genome into daughter cells. Microtubules, the major component of the spindle, are constantly recycled by two turnover mechanisms: dynamic instability of microtubule plus ends and treadmilling, or flux of tubulin dimers toward the pole. Thus, the critical function of chromosome segregatio...

[1] Two recent studies [Hotinski et al., 2001; Zhang et al., 2001] have modeled and discussed Late Permian ocean circulation and oxygenation. These studies have reached significantly different conclusions. Zhang et al. [2001] find that a ‘‘thermal mode’’ ocean circulation driven by cooling in polar latitudes is unlikely to support deep-sea anoxia, but a ‘‘haline mode’’ ocean circulation, a shal...