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L Rong

Publications and source records attributed to L Rong.

43 records · Page 3Linked to original sources
PubMed1993

Purification and characterization of the SRS2 DNA helicase of the yeast Saccharomyces cerevisiae.

The SRS2 gene of Saccharomyces cerevisiae was identified through mutational analysis as a suppressor of radiation-sensitive mutations in the error-prone repair pathway and by a hyper-recombination phenotype. Comparison of the derived amino acid sequence revealed the gene to have high homology to the bacterial DNA helicases UvrD and Rep (Aboussekhra, A., Chanet, R., Zgaga, Z., Cassier-Chauvat, C., Heude, M., and Fabre, F. (1989) Nucleic Acids Res. 17, 7211-7219). We have purified the SRS2 protein from Escherichia coli extracts by tagging the SRS2 gene with 6 carboxyl-terminal histidine residues and overexpressing the tagged protein in a pET-3c vector. Extracts were passed over a metal-chelating affinity chromatography column followed by gel filtration to obtain an enriched protein fraction. Sephacryl gel filtration of pooled fractions containing the SRS2 protein yielded purified SRS2 protein by Coomassie Blue stain of SDS-polyacrylamide gel electrophoresis gels. The purified SRS2 protein was found to have in vitro DNA-dependent ATPase and DNA helicase activities. The polarity of the helicase activity was determined to be 3' to 5', the same polarity as that found for the UvrD and Rep proteins. The carboxyl-terminal region of the protein is shown to contain a sequence for nuclear localization. Expression of the SRS2 in yeast was examined and found to be extremely low.

Adenosine Triphosphatases↗
PubMed1993

Regulation of the prfA transcriptional activator of Listeria monocytogenes: multiple promoter elements contribute to intracellular growth and cell-to-cell spread.

The prfA gene product is a transcriptional activator of Listeria monocytogenes determinants of pathogenicity. In this study, we provide direct evidence that the PrfA protein is a site-specific DNA-binding protein. Additionally, we describe the characterization of two classes of L. monocytogenes mutants which contain transposon insertions either in the prfA structural gene (exemplified by strain DP-L1075) or within the prfA promoter region (exemplified by strain DP-L973). Both mutants are completely avirulent and secrete greatly reduced levels of listeriolysin O and phosphatidylinositol-specific phospholipase C, and both are fully complemented by the introduction of prfA on a multicopy plasmid. The behaviors of the two mutants differ markedly within cultured macrophages. Following infection, no cytoplasmic growth was observed for DP-L1075 whereas DP-L973 escaped from the phagosome and grew in the cell cytoplasm. However, DP-L973 was defective in nucleation of actin filaments and spread to adjacent cells. Transcription of prfA in DP-L973 was directed from a single, previously unidentified promoter (prfAp2) located close to the prfA initiation codon. This promoter is therefore capable of providing sufficient prfA expression for escape from the host cell vacuole but is insufficient for wild-type levels of bacterially induced actin polymerization and cell-to-cell spread. Transcription directed from both prfAp1 and prfAp2 promoters was increased in the absence of a functional prfA gene product, suggesting that PrfA protein contributes to down-regulating its own expression.

Animals↗
PubMed1992

Changes in IGF-I and -II, IGF binding protein, and IGF receptor transcript abundance after uterine artery ligation.

Altered IGF activity may be one mechanism involved in the pathogenesis of intrauterine growth retardation (IUGR). We assessed the expression of IGF, IGF binding protein (IGFBP), and IGF receptor transcripts in liver, carcass, and placenta of fetal rats with IUGR resulting from unilateral uterine artery ligation. We found that uterine artery ligation on d 17 of gestation resulted in reduced body weight, liver weight, and placental weight on d 20 in the fetuses from the ligated uterine horn (UA-lig) compared with those from the opposite, nonligated uterine horn (UA-nonlig) and those from dams with no surgery or anesthesia. As assessed by solution hybridization, UA-lig fetuses exhibited significantly higher hepatic IGFBP-1, IGFBP-2, and IGF-II transcript abundance than UA-nonlig controls (increased 110, 50, and 31%, respectively). The only major difference among groups in carcass and placenta mRNA abundance was a 44% decrease in placental IGF-II expression in UA-lig pups compared with pups from dams that had had no surgery or anesthesia. Serum IGFBP, analyzed by ligand blot, showed a 2.4-fold increase in the doublet IGFBP-1/-2 band in UA-lig fetuses. Serum immunoreactive IGFBP-2 was unchanged among the groups, indicating that IGFBP-1 accounted for the increase in doublet intensity. Our results suggest that increased serum IGFBP-1 concentrations may decrease IGF activity in serum and thus inhibit IGF-stimulated cell proliferation or, by crossing the endothelial border, inhibit the activity of locally produced IGF. Decreased IGF-II expression in placenta also may contribute to decreased placental growth and, in turn, to IUGR.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The hyper-gene conversion hpr5-1 mutation of Saccharomyces cerevisiae is an allele of the SRS2/RADH gene.

The HPR5 gene has been defined by the mutation hpr5-1 that results in an increased rate of gene conversion. This mutation suppresses the UV sensitive phenotype of rad18 mutations in hpr5-1 rad18 double mutants by channeling the aborted repair events into a recombination repair pathway. The HPR5 gene has been cloned and is shown to be allelic to the SRS2/RADH gene, a putative DNA helicase. The HPR5 gene, which is nonessential, is tightly linked to the ARG3 locus chromosome X. The hpr5-1 allele contains missense mutation in the putative ATP binding domain. A comparison of the recombination properties of the hpr5-1 allele and the null allele suggests that recombination events in hpr5 defective strains can be generated by several mechanisms. We propose that the HPR5 gene functions in the RAD6 repair pathway.

Alleles↗
PubMed1990

picA, a novel plant-inducible locus on the Agrobacterium tumefaciens chromosome.

We used the transposon Mu dI1681 to identify genes on the Agrobacterium tumefaciens chromosome that are inducible by extracts from carrot roots. One such locus (picA, for plant inducible chromosomal), harbored by A. tumefaciens At156, was inducible 10- to 50-fold by these extracts. Mutation of picA had no detectable effect upon bacterial growth or virulence under laboratory assay conditions. However, A. tumefaciens cells harboring a mutated picA locus aggregated into long "ropes" when incubated with pea root tip cells. Such aggregation was not displayed by the parental strain A. tumefaciens A136. A preliminary characterization of the inducing compound in the carrot root extract suggests that the active substance is an acidic polysaccharide that is most likely derived from the pectic portion of the plant cell wall.

Chromosomes, Bacterial↗