Biomedical subjects
Publications and source records attributed to J L Tang.
Explore the source record for details and available documents.
The cosmid clone pIJ3020 containing DNA from the plant pathogenic bacterium Xanthomonas campestris pathovar campestris has previously been shown to complement a non-pathogenic mutant defective in synthesis of extracellular enzymes. The DNA cloned in pIJ3020 was analysed by mutagenesis with Tn5 and Tn5lac and by nucleotide sequencing. The results indicate that this region of the genome contains a cluster of genes, mutation in any of which results in failure of the enzymes and extracellular polysaccharide to be synthesized. The designation rpf (regulation of pathogenicity factors) is proposed for these genes. The nucleotide sequence of one gene (rpfC) predicts a protein product with homology to conserved domains of both sensor and regulator proteins of prokaryotic two-component regulatory systems, which are usually involved in regulating gene expression in response to environmental stimuli.
As an initial step in evaluating the role of tumor suppressor genes in leukemogenesis, we surveyed primary leukemia cells from 130 patients for possible deletion of the retinoblastoma susceptibility (Rb) gene by Southern blot analysis. Two of them clearly showed homozygous deletion of Rb alleles. The first patient was a pre-B acute lymphoid leukemia (ALL) associated with a cytogenetic translocation: t(14;16)(q24;q22). The deletion was located at the 3' portion of the Rb gene, very close to the site of Rb gene deletion recently identified in an ALL cell line. The absence of Rb110 protein was further confirmed by Western blot analysis. The second patient was a chronic myelomonocytic leukemia (CMMoL), terminated in acute blastic transformation. Deletion of the 5' portion of Rb gene was found in leukemic cells in the chronic stage. The results indicated that inactivation of the Rb gene occurred in certain cases of leukemia. Its significance warrants further study.
A recombinant plasmid pIJ3079 contains DNA sequences from Xanthomonas campestris pv campestris involved in coordinate negative regulation of production of the extracellular enzymes protease, endoglucanase, amylase and polygalacturonate lyase, and extracellular polysaccharide (EPS). Wild-type bacteria harbouring pIJ3079 and therefore carrying extra copies of the gene(s) therein showed reduced enzyme and EPS production and reduced aggressiveness to plants. Localised Tn5 mutagenesis of the corresponding region of the genome gave mutants producing higher levels of enzymes and EPS than the wild type, suggesting that the gene(s) may negatively regulate production in the normal cell. Enzyme and EPS production in the mutants was still dependent on previously characterised positive regulatory genes.
A multipurpose broad host range plasmid, pIJ3200, was constructed by inserting the polylinker-containing 445 bp PvuII fragment of Bluescript M13 into the EcoRI site of the cosmid pLAFR1. Using this vector a protease gene of Xanthomonas campestris pathovar campestris, previously cloned in the recombinant plasmid pIJ3070, was located by deletion to a 2.2 kb DNA region. Sequencing of the protease gene revealed an open reading frame encoding a 580 amino acid polypeptide with molecular weight of 57,000. The deduced amino acid sequence showed strong homology with the subtilisin family of serine proteases. This, together with its sensitivity to inhibition by phenylmethylsulphonyl fluoride, suggests that the enzyme belongs to this family of proteases.
Two proteases (PRT1 and PRT2) were fractionated from culture supernatants of wild-type Xanthomonas campestris pv. campestris by cation-exchange chromatography on SP-5PW. Inhibitor experiments showed that PRT 1 was a serine protease which required calcium ions for activity or stability or both and that PRT 2 was a zinc-requiring metalloprotease. PRT 1 and PRT 2 showed different patterns of degradation of beta-casein. The two proteases comprised almost all of the extracellular proteolytic activity of the wild type. A protease-deficient mutant which lacked both PRT 1 and PRT 2 showed considerable loss of virulence in pathogenicity tests when bacteria were introduced into mature turnip leaves through cut vein endings. This suggests that PRT 1 and PRT 2 have a role in black rot pathogenesis.
Major ABO-incompatible bone marrow transplantation (BMT) may be associated with delayed erythropoiesis. A 38-year-old man (blood group O) with chronic myelogenous leukemia received a BMT from his histocompatibility antigen (HLA) identical brother (blood group A). The pre-BMT anti-A titer of the patient was 1:4. The harvested marrow was depleted of RBC by 6% hydroxyethyl starch sedimentation and Ficoll-Hypaque gradient centrifugation. No acute hemolysis occurred after marrow infusion. Myeloid and megakaryocytic series engrafted promptly. However, delayed erythropoiesis up to day 266 was found. Prolonged presence of anti-A antibody was noted for more than 250 days after BMT, although the peak titer was only 1:8. After the reconstitution of bone marrow, the erythroid series was confirmed as donor origin (RBC cell typing A). It is proposed that the prolonged presence of anti-A antibody probably produced from the residual host B lymphocytes, would destroy the regenerating erythroid precursors. Also, use of cyclosporin A may be associated with higher rates of prolonged production of anti-A/B antibodies and the subsequent delayed erythropoiesis.
The interaction of herpes simplex virus type 1 (HSV-1) with murine macrophage cell lines was examined. The cell lines appeared to be moderately permissive for HSV-1 replication, though the yield of the virus was limited compared with that in Vero cells. Furthermore, the murine macrophage cell line SL-1, bearing Ia antigen, was persistently infected with HSV-1 for over one year, and was designated SL-1/KOS. Persistent infection could not be established in an Ia antigen-negative macrophage cell line, SL-4. In the SL-1/KOS culture, there was a small number of infected cells as revealed by infectious center assay. Treatment with monoclonal antibody against HSV-1 cured the persistent infection. Therefore maintenance of the persistent infection is considered to be due to a carrier culture consisting of a minority of infected cells and a majority of uninfected cells. In the SL-1/KOS cultures a low level of interferon (IFN) was found. When a large amount of exogenous recombinant murine IFN-beta (10(5)-10(6) international units/ml) was added to the culture, virus production diminished to undetectable levels. These results suggest that IFN plays an important role in the maintenance of persistent infection. In long-term persistently infected cultures, syncytium formation appeared and the virus from such cultures had a different DNA structure from that of the virus originally used for infection as revealed by restriction endonuclease analysis.
The effect of monoclonal antibody (MCA) to glycoprotein gB of herpes simplex virus (HSV) was studied in athymic nude mice inoculated with HSV intracutaneously in the midflank. HS1, the MCA used in the study, had a high neutralizing titer (1:2048) and had antibody-dependent cell-mediated cytotoxicity. HS1 was injected intraperitoneally at various intervals after HSV infection. HS1 injected 3 h after infection inhibited the development of skin lesions and most mice survived. Administration of HS1 at the time the local skin erosions appeared at the inoculated site (4-7 days after infection) was also effective, and in four of eight mice skin lesions completely healed. Furthermore, in three of four mice that survived, latent infections in the ganglia were also prevented as evidenced by the failure to detect HSV by co-cultivation with Vero cells. Administration of HS1 after the development of zosteriform skin lesions (5-9 days after infection) reduced virus in the ganglia and prolonged the survival time, though the disease was not completely arrested and all the mice died eventually.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
P53 mutation, through defects in repairing DNA damages, is associated with genomic instability. In 24 adult patients with relapsed acute lymphoblastic leukemia (ALL), the status of the p53 gene at different stages was serially followed by cytogenetic and polymerase-chain reaction/single strand conformation polymorphism (PCR/SSCP) analysis. P53 mutation was detected in 6 patients (25%) and all were at relapsed stages: 3 at first relapse, 2 at second relapse and one at refractory phase. Loss of the remaining p53 allele was demonstrated in 5 of them by cytogenetic and SSCP analysis. Furthermore, all of the p53 mutations were associated with appearance of complex cytogenetic changes (CCG), suggesting of cytogenetic instability (CGI). The frequency of acquiring p53 mutation during leukemic progression is significantly higher in patients with CGI than in patients without CGI (6/11 v 0/13, p = 0.003). P53 mutation was detected either concurrently (n = 2) or after (n = 4, 2(+)-18 months) appearance of CCG. The results suggest that p53 mutation is frequently involved during ALL relapse and is closely linked with cytogenetic instability.
Polymerase chain reaction and single strand conformation polymorphism (PCR-SSCP) analysis of the p53 tumor suppressor gene (from exon 2 to 9) was performed on samples from 47 adult patients with primary myelodysplastic syndrome (MDS). Point mutation was found in 5 (11%) patients: exon 7 in 3, exon 4 in 1 and intron 5 in 1. The frequency of p53 mutation was significantly higher at advanced stages (p = 0.048) and higher in patients with abnormal karyotypes (p = 0.023). Although all of the p53 mutations were detected at advanced stages, four of them were detected at initial diagnosis with very short survival. Sequential SSCP analysis in 20 transformed MDS patients revealed only one new p53 mutation during progression from early MDS phases. The results suggest that p53 mutation might occur as an early genetic event and is probably associated with rapid progression and poor survival in some MDS patients.