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The Methyltransferase from the LlaDII Restriction-Modification System Influences the Level of Expression of Its Own Gene. Lisa Lystbæk Christensen, 2004.The type II restriction-modification (R-M) system LlaDII isolated from Lactococcus lactis contains two tandemly arranged genes, llaDIIR and llaDIIM, encoding a restriction endonuclease (REase) and a methyltransferase (MTase), respectively . Interestingly, two LlaDII recognition sites are present in the llaDIIM promoter region, suggesting that they may influence the activity of the promoter through methylation status . In this study, separate promoters for llaDIIR and llaDIIM were identified, and the regulation of the two genes at the transcriptional level was investigated . DNA fragments containing the putative promoters were cloned in a promoter probe vector and tested for activity in the presence and absence of the active MTase . The level of expression of the MTase was 5- to 10-fold higher than the level of expression of the REase . The results also showed that the presence of M.LlaDII reduced the in vivo expression of the llaDIIM promoter (PllaDIIM) up to 1,000-fold, whereas the activity of the llaDIIR promoter (PllaDIIR) was not affected . Based on site-specific mutations it was shown that both of the LlaDII recognition sites within PllaDIIM are required to obtain complete repression of transcriptional activity . No regulation was found for llaDIIR, which appears to be constitutively expressed . Glyoxylate Regeneration Pathway in the Methylotroph Methylobacterium extorquens AM1. Natalia Korotkova, 2002. Inter- and Intraclonal Diversity of the Pseudomonas aeruginosa Proteome Manifests within the Secretome. Dirk Wehmhöner, 2003.The proteomes of cultured Pseudomonas aeruginosa isolates from chronically infected cystic fibrosis (CF) lungs were compared by using genetically divergent clones and isogenic morphotypes of one strain . Cellular extracts gave very similar protein patterns in two-dimensional gels, suggesting that the conserved species-specific core genome encodes proteins that are expressed under standard culture conditions in vitro . In contrast, the protein profiles of extracts of culture supernatants were dependent on the growth phase, and there were significant differences between clones . The profiles also varied within clonally related morphotypes from one CF patient, including a hyperpiliated small-colony variant . Mass spectrometry revealed that this variant overexpressed proteins secreted by the type I secretion system (including proteins involved in iron acquisition) and by the type III secretion system . Furthermore, the proteins in the supernatant extracts from the small-colony variant which were recognized by sera from different CF patients varied greatly . We concluded that the secretome expression is a sensitive measure of P . aeruginosa strain variation . Rhizobium leguminosarum Biovar viciae 1-Aminocyclopropane-1-Carboxylate Deaminase Promotes Nodulation of Pea Plants. Wenbo Ma, 2003.Ethylene inhibits nodulation in various legumes . In order to investigate strategies employed by Rhizobium to regulate nodulation, the 1-aminocyclopropane-1-carboxylate (ACC) deaminase gene was isolated and characterized from one of the ACC deaminase-producing rhizobia, Rhizobium leguminosarum bv . viciae 128C53K . ACC deaminase degrades ACC, the immediate precursor of ethylene in higher plants . Through the action of this enzyme, ACC deaminase-containing bacteria can reduce ethylene biosynthesis in plants . Insertion mutants with mutations in the rhizobial ACC deaminase gene (acdS) and its regulatory gene, a leucine-responsive regulatory protein-like gene (lrpL), were constructed and tested to determine their abilities to nodulate Pisum sativum L . cv . Sparkle (pea) . Both mutants, neither of which synthesized ACC deaminase, showed decreased nodulation efficiency compared to that of the parental strain . Our results suggest that ACC deaminase in R . leguminosarum bv . viciae 128C53K enhances the nodulation of P . sativum L . cv . Sparkle, likely by modulating ethylene levels in the plant roots during the early stages of nodule development . ACC deaminase might be the second described strategy utilized by Rhizobium to promote nodulation by adjusting ethylene levels in legumes .
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