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Tanigawa R, Shirokane M, Maeda Si, Omata T, Tanaka K, Takahashi H (2002) Transcriptional activation of NtcA-dependent promoters of Synechococcus sp. PCC 7942 by 2-oxoglutarate in vitro. P Natl Acad Sci USA 99: 4251–4255. Alfonso M, Kirilovsky D (2001) Redox Control of ntcA Gene Expression in Synechocystis sp. PCC 6803. Nitrogen Availability and NtcA Protein 1. Plant Physiol 125: 969–981. pmid:11161053 The next step in heterocyst development is the activation of hetR. Remarkably, null mutants of hetR do not produce heterocysts whereas an overexpression of hetR leads to an increased heterocyst frequency [ 27, 32, 33]. The transcription of hetR is induced by NtcA through the action of an intermediate, nrrA [ 28]. The DNA-binding activity of HetR requires its homodimerization [ 34, 35]. Multiple transcription factors related to heterocyst formation are up-regulated by HetR, including hetR itself [ 35], ntcA [ 36] and patS [ 35].
The work is structured as follows. First we present the main actors of the basic regulatory network and the different dynamical interactions that take place during the differentiation process. Then we develop a mathematical model for the unicellular reaction to nitrogen deprivation. Although a single cell model cannot provide a complete understanding of heterocyst formation, we analyze the main features that arise from the dynamical behavior of the system to gain insight about cell dynamics under different external conditions. Wisén S, Jiang F, Bergman B, Mannervik B (1999) Expression and purification of the transcription factor NtcA from the cyanobacterium Anabaena PCC 7120. Protein expres purif 17: 351–357. where D C is called the diffusion constant of the element C. Now, it is straightforward to introduce PatS and cN diffusion into the equations. The dynamics of cell i is characterized by the following set of equations: Murray JD (2003) Mathematical Biology II: Spatial Models and Biomedical Applications computational model predicts phenotype from genotype. New York: Springer-Verlag, third edition. A deletion mutant of hetL differentiates heterocysts as well as the wild-type strain ( Liu and Golden, 2002). The possibility that hetL is not essential for heterocyst differentiation and that only its overexpression affects the differentiation process was one of the hypotheses proposed to explain the phenotype of the hetL mutant. The second hypothesis was functional redundancy based on a crosstalk between HetL and another PRP ( Liu and Golden, 2002). The observation that at least one homolog of HetL (All4303) interacted with HetR, is rather in favor of functional redundancy. A global transcription study using RNA sequencing has shown that all4303 transcription is induced in response to nitrogen starvation ( Flaherty et al., 2011). The hetL gene has also been reported in this study to be induced after nitrogen starvation, which is consistent with our data. The other PRPs coding genes whose transcription has also been reported to be regulated in this condition are reported in Supplementary file 1. At this stage of our investigation, we cannot rule out that homologs of HetL may also be part of the PatS signaling, but the fact that the genetic suppressor screen for suppression of PatS inhibition selected only hetL would rather point to it as the principal factor involved in the differentiation process ( Liu and Golden, 2002). Because of the presence of multiple homologs, cross-complementation might occur when hetL happens to be mutated.
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It was important for us to choose a title which highlights the novelty that our study brings in relation to the state of art in the field. Nonetheless, we understand the importance of broad-significance titles and therefore decided to adopt the proposed one. Zhao, M. X. et al. Structural basis for the allosteric control of the global transcription factor NtcA by the nitrogen starvation signal 2-oxoglutarate. Proc. Natl. Acad. Sci. USA 107, 12487–92 (2010).
Buikema WJ, Haselkorn R: Characterization of a gene controlling heterocyst differentiation in the cyanobacterium Anabaena 7120. Genes Dev. 1991, 5 (2): 321-330. 10.1101/gad.5.2.321. A strain of cyanobacteria called Nostoc PCC 7120 can organise itself into long filaments of interconnected cells. Under certain conditions, one in every ten cells stops drawing its energy from the sun, and starts fixing atmospheric nitrogen instead. Exactly how the bacteria are able to ‘count to ten’ and organize themselves in such a precise pattern is still unclear. SARS-CoV-2 spike protein plays a key role in mediating viral entry and inducing host immune responses. It can adopt either an open or closed conformation based on the position of its receptor-binding domain (RBD). It is yet unclear what cause these conformational changes or how they influence the spike's functions. Here we show that Lys417 in the RBD plays dual roles in the spike's structure: it stabilizes the closed conformation of the trimeric spike by mediating inter-spike-subunit interactions; it also directly interacts with ACE2 receptor. Hence, a K417V mutation has opposing effects on the spike's function: it opens up the spike for better ACE2 binding while weakening the RBD's direct binding to ACE2. The net outcomes of this mutation are to allow the spike to bind ACE2 with higher probability, mediate viral entry more efficiently, but become more exposed to neutralizing antibodies. Given that residue 417 has been a viral mutational hotspot, SARS-CoV-2 may have been evolving to strike a balance between infection potency and immune evasion, contributing to its pandemic spread. The model is rounded off by coupling a number of cells in a one-dimensional array so that combined nitrogen and PatS can diffuse along the cellular chain. We have shown that one important ingredient affecting the dynamical behavior of the chain is noise, which plays a key role in onset of the pattern formation, i.e., the transition from the initial chain of vegetative cells to the steady state in which heterocysts coexist with vegetative cyanobacteria. Thus, the appearance of differentiation is, in our model, a pure stochastic event. The cooperative character of the filament is clear from the amount of noise needed to start the differentiation process which appears significantly smaller than that needed in isolated cells. The source of noise as well as its biological consequences is, nowadays a current topic of research [ 58]. In fact, at its initial state, differentiation of cells appears randomly along the filament, but shortly after its onset a characteristic distribution of heterocyst emerges. This distribution can be compared with the experimental one with a fairly good agreement [ 41].
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This year, we are confident that we could surpass last year’s achievement of RM4.25 billion business leads and also expect 40,000 visitors from 40 countries. Kumar K, Mella-Herrera RA, Golden JW: Cyanobacterial heterocysts. Cold Spring Harb Perspect Biol. 2010, 2 (4): a000315-10.1101/cshperspect.a000315. Kumar, K., Mella-Herrera, R. A. & Golden, J. W. Cyanobacterial heterocysts. Cold Spring Harb Perspect Biol. 2, a000315 (2010). He said that IGEM 2023, which is held from Oct 4 to Oct 6, and themed “Race Towards Net Zero: Leadership for Climate Action”, could play a decisive leadership role in accelerating and delivering the region’s net zero and energy transition agenda. Genes encoding HetR are conserved in conjunction with patS genes in both heterocystous and nonheterocystous cyanobacteria [ 16]. PatS and HetR are thought to act together to regulate the spacing of heterocysts [ 8],[ 17],[ 18]. A small pentapeptide RGSGR motif in PatS and HetN is sufficient to inhibit heterocyst formation [ 12]-[ 14],[ 19] and PatS peptides can bind directly to the HetR dimer with PatS-6 binding the tightest [ 17],[ 20]. Because HetR and PatS are conserved in cyanobacteria that do not form heterocysts, and because HetR is expressed at low levels in vegetative cells, it is possible that HetR and PatS serve a function in addition to their known roles in heterocyst development [ 16]. HetR has two protein interaction domains, suggesting that other proteins may modulate HetR's activity and DNA binding [ 6]. However, very little is known about HetR's possible role outside heterocyst development or about its target genes in nonheterocystous cyanobacteria.
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