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The Stigmatella aurantiaca Homolog of Myxococcus xanthus High-Mobility-Group A-Type Transcription Factor CarD: Insights into the Functional Modules of CarD and Their Distribution in Bacteria. Marķa L. Cayuela, 2003.Transcriptional factor CarD is the only reported prokaryotic analog of eukaryotic high-mobility-group A (HMGA) proteins, in that it has contiguous acidic and AT hook DNA-binding segments and multifunctional roles in Myxococcus xanthus carotenogenesis and fruiting body formation . HMGA proteins are small, randomly structured, nonhistone, nuclear architectural factors that remodel DNA and chromatin structure . Here we report on a second AT hook protein, CarDSa, that is very similar to CarD and that occurs in the bacterium Stigmatella aurantiaca . CarDSa has a C-terminal HMGA-like domain with three AT hooks and a highly acidic adjacent region with one predicted casein kinase II (CKII) phosphorylation site, compared to the four AT hooks and five CKII sites in CarD . Both proteins have a nearly identical 180-residue N-terminal segment that is absent in HMGA proteins . In vitro, CarDSa exhibits the specific minor-groove binding to appropriately spaced AT-rich DNA that is characteristic of CarD or HMGA proteins, and it is also phosphorylated by CKII . In vivo, CarDSa or a variant without the single CKII phosphorylation site can replace CarD in M . xanthus carotenogenesis and fruiting body formation . These two cellular processes absolutely require that the highly conserved N-terminal domain be present . Thus, three AT hooks are sufficient, the N-terminal domain is essential, and phosphorylation in the acidic region by a CKII-type kinase can be dispensed with for CarD function in M . xanthus carotenogenesis and fruiting body development . Whereas a number of hypothetical proteins homologous to the N-terminal region occur in a diverse array of bacterial species, eukaryotic HMGA-type domains appear to be confined primarily to myxobacteria . Wind River Conference on Prokaryotic Biology—2002. Kenneth W. Bayles, 2003. The Product of a Developmental Gene, crgA, That Coordinates Reproductive Growth in Streptomyces Belongs to a Novel Family of Small Actinomycete-Specific Proteins. Ricardo Del Sol, 2003.On solid media, the reproductive growth of Streptomyces involves antibiotic biosynthesis coincident with the erection of filamentous aerial hyphae . Following cessation of growth of an aerial hypha, multiple septation occurs at the tip to form a chain of unigenomic spores . A gene, crgA, that coordinates several aspects of this reproductive growth is described . The gene product is representative of a well-conserved family of small actinomycete proteins with two C-terminal hydrophobic-potential membrane-spanning segments . In Streptomyces avermitilis, crgA is required for sporulation, and inactivation of the gene abolished most sporulation septation in aerial hyphae . Disruption of the orthologous gene in Streptomyces coelicolor indicates that whereas CrgA is not essential for sporulation in this species, during growth on glucose-containing media, it influences the timing of the onset of reproductive growth, with precocious erection of aerial hyphae and antibiotic production by the mutant . Moreover, CrgA subsequently acts to inhibit sporulation septation prior to growth arrest of aerial hyphae . Overexpression of CrgA in S . coelicolor, uncoupling any nutritional and growth phase-dependent regulation, results in growth of nonseptated aerial hyphae on all media tested, consistent with a role for the protein in inhibiting sporulation septation . The Nucleotide Transporter of Caedibacter caryophilus Exhibits an Extended Substrate Spectrum Compared to the Analogous ATP/ADP Translocase of Rickettsia prowazekii. Robin M. Daugherty, 2004.The two obligate intracellular alphaproteobacteria Rickettsia prowazekii and Caedibacter caryophilus, a human pathogen and a paramecium endosymbiont, respectively, possess transport systems to facilitate ATP uptake from the host cell cytosol . These transport proteins, which have 65% identity at the amino acid level, were heterologously expressed in Escherichia coli, and their properties were compared . The results presented here demonstrate that the caedibacter transporter had a broader substrate than the more selective rickettsial transporter . ATP analogs with modified sugar moieties, dATP and ddATP, inhibited the transport of ATP by the caedibacter transporter but not by the rickettsial transporter . Both transporters were specific for di- and trinucleotides with an adenine base in that adenosine tetraphosphate, AMP, UTP, CTP, and GTP were not competitive inhibitors . Furthermore, the antiporter nature of both transport systems was shown by the dependence of the efflux of [  -32P]ATP on the influx of substrate (ATP but not dATP for rickettsiae, ATP or dATP for caedibacter) .
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