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Actinomycetes are high GC Gram-positive, mainly soil-inhabiting bacteria and many of them show a filamentous growth. Filamentous actinomycetes are often characterized by a complex morphological development. However, although morphological development of Streptomyces has been studied extensively and deeply, almost no genetic studies of the morphogenesis of other filamentous actinomycetes have been conducted even though some of them show more complex morphological differentiation than Streptomyces. Actinoplanes missouriensis, a well-characterized member of the genus, forms globose or subglobose terminal sporangia that contain a few hundred spherical spores each on sporangium-forming HAT (humic acid-trace element) agar. AmBldD controls the timing of the transition from vegetative growth to sporangium formation. The bacterial flagellum is a complex molecular machine, and it is composed of the following substructures: cytoplasmic ring (C ring), membrane and supramembrane ring (MS ring), rod, hook and filament. In addition to these, Gram-negative bacteria also have a peptidoglycan ring (P ring) and lipopolysaccharide ring (L ring). Flagellar biogenesis is tightly regulated at the transcriptional level. To elucidate the regulatory mechanism of flagellar gene expression in A. missouriensis, researcher focused on a gene immediately adjacent to the chemotaxis 1 (che-1) gene cluster flanked with the flagellar gene cluster. The gene (AMIS76580) encodes a protein that is predicted to function as a two-component regulatory system response regulator. Herein, researcher name AMIS76580 TcrA for its predicted function.
Fig1. Proposed model of the regulatory cascade of gene expression for the morphological development in A. missouriensis.
(Molecular Microbiology, 2018.)
TcrA (232 amino acid residues) contains a response regulator receiver domain and a transcriptional regulatory DNA-binding domain with a winged helix-turn-helix motif in its N-terminal and C-terminal regions, respectively, and is a member of the OmpR-like response regulators. TcrA is considered an orphan response regulator, because there is no sensor histidine kinase gene near the tcrA locus. tcrA expression is kept at low levels in vegetative growth but is activated during sporangium formation. Then, it significantly decreases through the process of sporangium dehiscence and reaches the basal level in germinating zoospores.
Researcher determined the transcriptional start points of tcrA to be 144 and 181 nucleotides upstream from the translational start codon by high resolution S1 nuclease mapping. Interestingly, researcher found a palindromic sequence similar to the AmBldD box in the promoter region of tcrA, suggesting that AmBldD directly regulates the transcription of tcrA.
Phosphorylation at Asp-52 by a sensor histidine kinase(s) is required for the in vivo function of TcrA. Researcher think that the germination tubes cause apparently very small cells observed in the TEM image of the ∆tcrA mutant sporangium; the diameter of germination tube is much smaller than that of spore. TcrA is required for the formation of sporangia that are mature enough to dehisce and release spores.
The transcriptional levels of 244 genes were changed, with 204 and 40 genes being down- and up-regulated, respectively, in the ∆tcrA mutant. This indicated that TcrA mainly functions as a transcriptional activator similar to other known two-component system response regulators. TcrA activates many genes involved in signal transduction not only for motility of zoospores but also for sporangium formation, maturation and/or dehiscence.
The RNA-Seq analysis showed that the transcriptional levels of all flagellar genes were down-regulated in the ∆tcrA strain (1.4-fold at least, 59.6-fold on average). Researcher examined the transcriptional levels of nine flagellar genes in the wt and ∆tcrA strains by qRT-PCR, further verifying that TcrA activates the transcription of these flagellar genes; all of them were down-regulated in the ∆tcrA strain (from 10 to 103-fold). TcrA-NHis was shown to bind to all five TcrA box-containing sequences found in the regulatory regions for flagellar genes.
TcrA directly regulates fliA1 and fliA3. The EMSAs and competitive EMSAs showed that TcrA-NHis bound to the 41 TcrA box-containing fragments in total. TcrA directly regulates the expression of the 34 transcriptional units that contain TcrA boxes categorized into groups A, B and D. It should be noted that such categories do not reflect the transcriptional activation levels of the target genes.
During vegetative growth, tcrA is repressed by AmBldD, which serves as the global transcriptional repressor of the genes involved in sporangium formation. In response to the transition from vegetative growth to sporangium formation, TcrA is produced and supposedly phosphorylated to activate many genes presumably responsible for sporangium formation. Researcher propose that TcrA directly activates the transcription of 34 transcriptional units, of which 20 possess a putative FliA-recognizing promoter. TcrA is a global transcriptional activator that controls many aspects of sporangium formation in A. missouriensis. Considering that TcrA orthologues are highly conserved among Actinoplanes bacteria, researcher expect that the global regulation of TcrA for pleiotropic phenotypic features is common in this genus.
| Target | Cat. No. | Product Name | Expression System | Tag/Conjugate | Application | |
| Maltokinase | DAGA-3436 | Recombinant Actinoplanes missouriensis mak1 [His], E. coli | E. coli | His | N/A | Inquiry |
| DAGA-3437 | Recombinant Actinoplanes missouriensis mak1 [His] | Mammalian cell | His | N/A | Inquiry | |
| DAGA-3438 | Recombinant Actinoplanes missouriensis mak1 [His], Baculovirus | Baculovirus | His | N/A | Inquiry |
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