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Biomedical subjects

J C Shu

Publications and source records attributed to J C Shu.

7 recordsLinked to original sources
PubMed2003

Dietary methionine requirement of the Chinese egg-laying duck.

1. The dietary methionine requirement of egg-laying ducks was assessed by feeding diets supplemented with graded levels of DL-methionine (0, 4, 8, 12, 16 g/kg dietary protein) for 8 weeks. The basal diet contained 175 g protein and 2.6 g methionine per kg feed (or 14.9 g/kg protein) and an estimated ME of 11.5 MJ/kg. 2. A total of 800 Shaoxin laying ducks (420 d old) were randomly divided into 5 groups of 160 each and fed in 4 separate pens. 3. Dietary supplementation of methionine significantly increased egg production and feed conversion efficiency. 4. Dietary methionine requirement for optimum egg production was estimated to be 25.7 g/kg of dietary protein or 4.5 g/kg of the diet or 380 mg/bird-d. 5. Methionine supplementation increased the methionine level in plasma, and the free glutamic acid and aspartic acid concentrations in plasma were quadratically related to dietary methionine levels. Increasing dietary methionine had little effect on egg quality characteristics.

Amino Acids↗
PubMed2001

Bacillus subtilis mutations that alter the pathway of phosphorylation of the anti-anti-sigmaF factor SpoIIAA lead to a Spo- phenotype.

Sigma-F, the first sporulation-specific transcription factor of Bacillus subtilis, is regulated by an anti-sigma factor SpoIIAB, which can also act as a protein kinase that phosphorylates the anti-anti-sigma factor SpoIIAA. The time course of phosphorylation reaction is biphasic, a fact that has been interpreted in terms of a mechanism for sequestering SpoIIAB away from sigmaF and thus allowing activation of sigmaF when needed. Site-directed mutagenesis of SpoIIAA has allowed us to isolate two mutants that cannot activate sigmaF and which are therefore Spo-. The two mutant SpoIIAA proteins, SpoIIAAL61A and SpoIIAAL90A, are phosphorylated with linear kinetics; in addition they are less able to form the stable non-covalent complex that wild-type SpoIIAA makes with SpoIIAB in the presence of ADP. The phosphorylated form of SpoIIAAL90A was hydrolysed by the specific phosphatase SpoIIE at the same rate as wild-type SpoIIAA-P, but the rate of hydrolysis of SpoIIAAL61A-P was much slower. The secondary structure and the global fold of the mutant proteins were unchanged from the wild type. The results are interpreted in terms of a model for the wild type in which SpoIIAB, after phosphorylating SpoIIAA, is released in a form that is tightly bound to ADP and which then makes a ternary complex with an unreacted SpoIIAA. We propose that it is the inability to make this ternary complex that deprives the mutant cells of a means of keeping SpoIIAB from inhibiting sigmaF.

Adenosine Diphosphate↗
PubMed1997

Effect of glucose concentration on swimming motility in enterobacteria.

Since the observation that glucose prevents the synthesis of flagella in Escherichia coli was first reported in 1967, many studies have addressed the underlying mechanism. Currently, it is thought that an increase in glucose concentration decreases the intracellular CRP/cAMP concentration. This leads to an inhibitory effect on the expression of the flhD operon, the master operon for flagella synthesis. In our study on defining factors influencing the cell differentiation of Serratia marcescens, glucose catabolite repression of hag expression and swimming/swarming motility was not observed. Further experiments using a simple swimming motility assay extended this observation to other members of Enterobacteriaceae. Although the underlying mechanism is still uncharacterised, our results suggest that glucose catabolite repression of swimming motility may not be a common phenomenon in Enterobacteriaceae.

DNA-Binding Proteins↗
PubMedDate not supplied

Role of flhDC in the expression of the nuclease gene nucA, cell division and flagellar synthesis in Serratia marcescens.

We investigated in Serratia marcescens the functions of the flhDC operon, which controls motility and cell division in enteric bacteria. Included in our evaluations were investigation of cell division, flagellar synthesis and regulation of the expression of nuclease (encoded by the nucA(Sm) gene, one of the virulence factors). Interruption of the chromosomal flhDC operon in S. marcescens CH-1 resulted in aberrant cell division and loss of nuclease and flagella. Expression of nucA(Sm) and other mutated phenotypes was restored in the flhDC mutant by the induction of overexpression of flhDC in a multicopy plasmid. Multicopied flhDC also induced the formation of differentiated cells (polyploid aseptate cells with oversynthesis of peritrichous flagella) in broth culture using minimal growth medium. Expression of the flhDC operon showed positive autoregulation, and was growth phase dependent (upregulated in early log phase). In addition, flhDC expression was inhibited when the temperature increased from 30 to 37 degrees C, and when osmolarity was increased, but was not influenced by glucose catabolite repression. These results show that FlhD/FlhC is a multifunctional transcriptional activator involved in the process of cell differentiation, swarming and virulence factor expression.

Amino Acid Sequence↗
PubMedDate not supplied

The role of RsmA in the regulation of swarming motility in Serratia marcescens.

Swarming motility is a multicellular phenomenon comprising population migration across surfaces by specially differentiated cells. In Serratia marcescens, a network exists in which the flhDC flagellar regulatory master operon, temperature, nutrient status, and quorum sensing all contribute to the regulation of swarming motility. In this study, the rsmA (repressor of secondary metabolites) gene (hereafter rsmA(Sm)) was cloned from S. marcescens. The presence of multicopy, plasmid-encoded rsmA(Sm) expressed from its native promoter in S. marcescens inhibits swarming. Synthesis of N-acylhomoserine lactones, presumably by the product of smaI (a luxI homolog isolated from S. marcescens), was also inhibited. Knockout of rsmA(Sm) on the S. marcescens chromosome shortens the time before swarming motility begins after inoculation to an agar surface. A single copy of the chromosomal PrsmA(Sm)::luxAB reporter of rsmA(Sm) transcription was constructed. Using this reporter, the roles of the flhDC flagellar regulatory master operon, temperature and autoregulation in the control of rsmA(Sm) expression were determined. Our findings indicate that RsmA(Sm) is a component of the complex regulatory network that controls swarming.

Amino Acid Sequence↗