poles at division implies that cell polarity must be re-established in the stalked progeny and reversed in the swarmer progeny. The C. crescentus life cycle is governed by regulators such as TipN, a cell cycle protein. Yale University's data strongly suggest a model in which TipN regulates the orientation of the polarity axis by providing a positional cue from the preceding cell cycle. In this model TipN specifies the site of the most recent division by identifying the new pole. The cell uses this positional information as a source of intracellular asymmetry to establish and maintain the orientation of the polarity axis, which is crucial for polar morphogenesis and division. Recruitment of TipN to the nascent poles at the end of the division cycle redefines the identity of the poles and resets the correct polarity in both future daughter cells (with a polarity reversal in the swarmer cell). The cell cycle–regulated synthesis and removal of these polarly localized structures have provided a rich playground for the identification of landmark proteins important for their proper localization. TipN has two transmembrane regions in the N-terminal region and a large C-terminal coiled-coil domain. TipN homologues are present in other alpha-proteobacteria. TipN localizes to the new pole in both daughter cells after division and relocalizes to the cell division site in the late predivisional cell. Therefore, both daughter cells have TipN at the new pole after division. The landmark protein TipN is essential for the proper placement of the flagellum. Mutants lacking TipN make serious mistakes in development. Instead of making a single flagellum at the correct cell pole , the cell makes multiple flagella at various locations, even on the stalk. Cell development involves many such proteins working together. Fig#1 shows how TipN interact with two other polar proteins : the flagellar marker PodJ , and the stalk marker DivJ. References External links Caulobacter crescentus Bacterium makes nature's strongest glue Caulobacterales Bacteria described in 1964