5,169 research outputs found
Second messenger mediated spatiotemporal control of cell cycle and development
No full textDuring the biphasic life cycle of Caulobacter crescentus motile, free-living swarmer
cells differentiate into sessile, surface attached stalked cells. The swarmer cell is
replication inert and is unable to divide. During the swarmer-to-stalked cell
differentiation, degradation of CtrA, a master regulator that blocks replication initiation,
leads the onset of chromosome replication. After this obligate cell differentiation step,
which is mainly regulated by the degradation of the master cell cycle regulator CtrA,
stalked cells immediately initiate their chromosome replication. Recently, dynamic colocalization
of CtrA and its protease ClpXP to cell pole was proposed as a timing
mechanism for cell cycle-dependent CtrA degradation.
We have identified the response regulator PopA as an essential regulator for CtrA
sequestration to the incipient stalked cell pole and for subsequent CtrA degradation by
the nearby ClpXP protease complex. Time laps fluorescence microscopy of PopA-GFP
showed that PopA itself dynamically sequesters to the cell poles during the C.
crescentus cell cycle. While PopA sequestration to the flagellated pole depends on
PodJ, a swarmer pole specificity factor, localization to the incipient stalked pole
depends on the C-terminal GGDEF output domain of PopA. We demonstrate that in
contrast to most GGDEF domain proteins, PopA lacks diguanylate cyclase activity.
Instead, PopA functions as cyclic di-GMP effector protein, which specifically binds the
bacterial second messenger at a conserved binding site (I-site) within the GGDEF
domain. An intact PopA I-site is required for PopA sequestration to the incipient stalked
pole as well as for CtrA degradation during the cell cycle. PopA directs CtrA to the
ClpXP occupied cell pole via a direct interaction with an adaptor protein, RcdA. Based
on this we postulate that c-di-GMP bound PopA facilitates the dynamic distribution of
CtrA to the cell pole where it s degraded by ClpXP. This is the first report that links cdi-
GMP to protein dynamics and cell cycle control in bacteria.
In addition to its prominent role in cell cycle control, PopA was identified as novel
component of the complex regulatory network that orchestrates polar development in
C. crescentus. PopA, together with PleD and DgcB, two active diguanylate cyclases,
controls cell motility, holdfast formation and surface attachment. Our data suggest that
PopA interferes with PleD and DgcB to coordinate cell motility, stalk biogenesis,
holdfast formation and finally surface attachment. Based on this, we propose that PopA is a bifunctional protein, involved in control and coordination of C. crescentus cell
cycle and development
Insights into the activation mechanism of PopA, a cyclic di-GMP effector protein involved in cell cycle and development of "Caulobacter Crescentus"
No full textIn Caulobacter crescentus, a complex network integrating cyclic di-GMP and Phosphorylation-dependent signals controls the proteolysis of key regulatory proteins to drive cell cycle and polar morphogenesis. The c-di-GMP input is processed by the effector protein PopA. Upon binding of c-di-GMP, PopA is sequestered to the old cell pole where it recruits the replication and cell division inhibitors CtrA and KidO and mediates their destruction by the polar ClpXP protease prior to entry into S-phase. In addition to its role at the stalked cell pole, PopA localizes to the opposite cell pole in dependence of the general topology factor PodJ where it exerts a yet unknown function.
Here we address the activation and polar sequestration mechanism of PopA guided by an existing activation model for the highly homologous c-di-GMP signaling protein PleD. PopA and PleD do not only share an identical domain organization (Rec1-Rec2-GGDEF), but also show similar spatio-temporal behavior during the cell cycle. While PleD is activated and targeted to the old cell pole via phosphorylation-induced dimerization, we show that PopA stalked pole function is phosphorylation-independent and requires c-di-GMP binding as a primary input signal for activation and polar localization. c-di-GMP binds to conserved primary and secondary I-sites within the PopA GGDEF domain and we show that intact binding sites are required for PopA positioning and function. This suggests that c-di-GMP-dependent crosslinking of adjacent GGDEF domains contributes to the localization of an active PopA dimer to the cell pole. Consistent with this, we demonstrate that the GGDEF domain encodes the polar localization signal(s), while the N-terminal receiver domains serve as interaction platform for downstream components that are actively recruited by PopA.
Among these downstream factors is RcdA, a small mediator protein that interacts with the first PopA receiver domain and helps to recruit and degrade CtrA and KidO. In a screen for additional components of the PopA pathway we identify two novel proteins that directly interact with PopA, CC1462 and CC2616. CC1462 is a ClpXP substrate that requires PopA for polar positioning and subsequent degradation during swarmer-to-stalked cell transition. Although located in a flagellar gene cluster, deletion of CC1462 did not affect flagellar assembly and function. Its cellular role as well as the significance of its cell cycle-dependent degradation requires further studies. CC2616, the second PopA interaction partner, is not proteolytically processed and thus belongs to another class of PopA-dependent substrates. CC2616 is annotated as guanine deaminase, which is predicted to catalyze the conversion from guanine to xanthine thereby irreversibly removing guanine based nucleotides from a cellular pool. A CC2616 deletion leads to increased attachment and decreased motility, a phenocopy of strains with elevated c-di-GMP levels. It is not clear whether CC2616 indeed has deaminase activity or whether it has adopted a novel function.
Taken together, this work provides insight into the activation mechanism of a c-di-GMP effector protein. We propose that PopA has evolved through gene duplication from its ancestor, the catalytic PleD response regulator but has lost catalytic activity of the diguanylate cyclase domain. Moreover, PopA has adopted an inverse intra-molecular information transfer originating through c-di-GMP binding at the C-terminal GGDEF domain, which in turn activates the N-terminal receiver stem to serve as platform for downstream partner recruitment
Activation and polar sequestration of PopA, a c-di-GMP effector protein involved in Caulobacter crescentus cell cycle control
No full textWhen Caulobacter crescentus enters S-phase the replication initiation inhibitor CtrA dynamically positions to the old cell pole to be degraded by the polar ClpXP protease. Polar delivery of CtrA requires PopA and the diguanylate cyclase PleD that positions to the same pole. Here we present evidence that PopA originated through gene duplication from its paralogue response regulator PleD and subsequent co-option as c-di-GMP effector protein. While the C-terminal catalytic domain (GGDEF) of PleD is activated by phosphorylation of the N-terminal receiver domain, functional adaptation has reversed signal transduction in PopA with the GGDEF domain adopting input function and the receiver domain serving as regulatory output. We show that the N-terminal receiver domain of PopA specifically interacts with RcdA, a component required for CtrA degradation. In contrast, the GGDEF domain serves to target PopA to the cell pole in response to c-di-GMP binding. In agreement with the divergent activation and targeting mechanisms, distinct markers sequester PleD and PopA to the old cell pole upon S-phase entry. Together these data indicate that PopA adopted a novel role as topology specificity factor to help recruit components of the CtrA degradation pathway to the protease specific old cell pole of C. crescentus
Efficient Algorithms for Counting Gapped Palindromes
No full textA gapped palindrome is a string uvu^{R}, where u^{R} represents the reverse of string u. In this paper we show three efficient algorithms for counting the occurrences of gapped palindromes in a given string S of length N. First, we present a solution in O(N) time for counting all gapped palindromes without additional constraints. Then, in the case where the length of v is constrained to be in an interval [g, G], we show an algorithm with running time O(N log N). Finally, we show an algorithm in O(N log² N) time for a more general case where we count gapped palindromes uvu^{R}, where u^{R} starts at position i with g(i) ≤ v ≤ G(i), for all positions i
IMPROVING SOCIAL MEDIA PRACTICES FOR B-TO-B MARKET
No full textB2B social networks are today at the heart of all discussions, whether at the professional or personal level. Indeed, there are more and more controversies around these tools of commu-nication. However, in many cases, social networks are a real advertising boost. Today, social networks in B2B are a real factor of influence and they are an integral part of a digital market-ing strategy.
An inductive research approach was applied in this thesis and a qualitative research method was used for collecting the data. The qualitative research was conducted through four inter-views, three of them with three different distributors for Kekkilä Professional and one inter-view with the marketing manager. The data was collected data from both primary and second-ary sources. Primary data was collected from the interviews and the secondary method in-cluded data collected from the author’s own experience, books and electric sources.
In the theoretical part, the author explains the meaning of digital marketing, social media mar-keting, which are the social media channels, and which social networks will be the most im-portant for Kekkilä Professional to focus on when the company will develop its social media practices for the B2B market in the future. The author continues with theories about particulari-ties for the B2B market. A SWOT analysis was created for the case company and a develop-ment plan for Kekkilä Professional is presented.
In conclusion, Kekkilä Professional should focus on social media channels (LinkedIn, Face-book and Twitter) in the future for the B2B market because using social media is essential in the digital communication era. However, it is important to take the time to design a complete social media strategy to use them wisely and to achieve the goals that Kekkilä Professional has set.
Social media has earned its acclaim in the B2B market and these channels became essential to explore, to generate traffic and to create leads
Euscelidia popa Dikow 2003, sp. n.
No full textEuscelidia popa sp. n. Fig. 60 Etymology: Noun in apposition that refers to the type locality Mt. Popa, Myanmar. Diagnosis: The species is distinguished from congeners by the overall yellow to gold pruinosity and setae and the densely arranged microtrichia on the wings. Description: Head: Black; fc gold pruinose, fc gib indistinct, mystax yellow, many macrosetae; prob and plp brownish-black, prob with white setae, plp with yellow and brown setae; oc tr apruinose; occ yellow pruinose, setae yellow; Antennae - scp brown, brown setae ventrally; ped brown, brown setae ventrally and dorsally, white pruinose; pped ventrally light brown, brown dorsally, white pruinose; apsel brown. Thorax: Black; ppro peg large, yellow pruinose; sct bluish-black, antero-laterally red, gold pruinose, apruinose indistinct spots laterally, yellow setae scattered on surface; macrosetae: black, 1 npl s, 1 spal s; mesopleura gold pruinose; sctl gold pruinose, ds sctl s and sctl s long, yellow; Legs - light brown to brown; fem light brown, setae white, meta fem slightly clubbed, club with brown setae; pro and meso tib light brown, yellow stripe anteriorly, meta tib in proximal half light brown, distal half brown, yellow stripe anteriorly; first tar yellow, brown distad, remaining tar brown, black setae; emp short, nearly a quarter of length of clw; Wings - densely covered with microtrichia, cells c, sc, proximal half of r 1, br, and bm dark brown, R 2+3 bent anteriorly and R 4 bent posteriorly (distal tip of cell r 2 widened); ptero distinct, brown; cell d terminating in 2 veins, cell a 1 nearly closed; hlt light brown. Abdomen: Dark brown; T predominantly brown pruinose, anterior, lateral, and posterior margins grey pruinose, T1 with long yellow setae laterally, T2 with yellow setae laterally, remaining T with yellow or brown setae, S grey pruinose; ơ terminalia - ơơ specimens unknown. Type material - The ^ holotype is labelled ‘Upper Burma [Myanmar] Mt. Popa 600– 1000 m, X. u. XI. 37 [x.–xi.1937] leg. G. Heinrich (yellow label) / Brit. Mus. 1939-186 / HOLOTYPE Euscelidia popa sp. nov. det. T. Dikow 2001 (red label)’. The specimen is directly mounted, is in excellent condition, and is deposited in the BMNH. Type locality and distribution (Fig. 60): Myanmar, Mount Popa, 20 53'N 95 14'E. Myanmar. Remarks: Despite the fact this species is only known from a single female I decided to describe it as a new species because it is easily distinguished from all other Oriental species by the overall gold and yellow appearance.Published as part of Dikow, Torsten, 2003, Revision of the genus Euscelidia Westwood, 1850 (Diptera: Asilidae: Leptogastrinae), pp. 1-131 in African Invertebrates 44 (2) on pages 96-97, DOI: 10.5281/zenodo.791118
Power Converters, Electric Drives and Energy Storage Systems for Electrified Transportation and Smart Grid Applications
No full textThe proposed special issue (SI) has invited submissions related to renewable energy, energy storage, power converters and electric drive systems for electrified transportation and smart grid applications [...
A Galois correspondence for compact groups of automorphisms of von Neumann algebras with a generalization to Kac algebras
No full textAbstractLetMbe a factor with separable predual andGa compact group of automorphisms ofMwhose action is minimal, i.e.,MG′∩M=C, whereMGdenotes theG-fixed point subalgebra. Then every intermediate von Neumann algebraMG⊂N⊂Mhas the formN=MHfor some closed subgroupHofG. An extension of this result to the case of actions of compact Kac algebras on factors is also presented. No assumptions are made on the existence of a normal conditional expectation ontoN
M-regularity and the fourier-mukai transform
No full textThis is a survey of M-regularity and its applications, expanding on lectures given by the second author at the Seattle conference, in August 2005, and at the Luminy workshop "Geometrie Algebrique Complexe", in October 2005
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