SAAS bulletin, biochemistry and biotechnology最新文献

This article reviews the findings on temperature sensitivity of equine herpesvirus isolates with an emphasis on equine herpesvirus 3, etiological agent of equine coital exanthema. The hypothesis is presented that the relative apathogenic nature of this herpesvirus may be an indirect result of its inability to synthesize and/or process glycoproteins needed by the virus to produce infectious virions at the normal body temperature of its natural host. It is suggested that equine herpesvirus 3 is the more evolved and naturally attenuated member of the equine herpesviruses.

Tumors that formerly were uniformly fatal can now be cured by cancer chemotherapy. However, successful anticancer therapy is faced by many obstacles, such as excessive normal tissue toxicity and drug resistance. Tumor drug resistance may be either intrinsic or acquired. The multidrug resistance (MDR) is a unique phenomenon and is characterized by tumor resistance to various structurally unrelated drugs. Known mechanisms for MDR include overexpression of a membrane P-glycoprotein 170 and elevated cellular levels of reducing agents, such as glutathione (GSH). Currently available strategies for overcoming drug resistance include competitive inhibitors of the P-glycoprotein 170, inhibitors of GSH synthesis, and adjuvant therapy with hyperthermia. Development of drug resistance is analogous to a physiological detoxification mechanism and may continue to limit the effectiveness of cancer chemotherapy in the near future.

The Bacillus subtilis plasmid pKBT1, the product of in vivo recE4-independent recombinal events, contains segments derived from pUB110 and the B. subtilis chromosome. To determine whether the pUB110 sequence is intact in PKBT1, two 1 kb fragments, each containing a site at which chromosomal and pUB110 sequences are joined, were cloned and sequenced. Sequencing data revealed that: 1). An intact copy of pUB110 is present in pKBT1; 2) The apparent recombination sites were adjacent to the Bam HI-generated ends of pUB110 sequences; 3) pTL12-derived sequences from the original transforming DNA were limited to no more than 1 bp outside the Bgl II recognition sequence; 4) Recombination sites at both ends of pUB110 contain a 19 bp inverted repeat with 15 homologous nucleotides. These findings suggest a site-specific mechanism acting during in vivo formation of pKBT1.

Intramolecular thiolester bonds in apolipoprotein B (ApoB) were studied using [14C]methylamine (MA) to cleave the thiolester and [3H]- or [14C]iodoacetate (IA) to titrate the newly generated sulfhydryls. Covalent incorporation of [14C]MA and [3H]carboxylmethyl group into the previously carboxymethylated LDL or the reduced and carboxymethylated ApoB was observed and both radioactivities coincided with ApoB-100 band on SDS-polyacrylamide gel electrophoresis. The [14C]MA-labeled ApoB was completely trypsinized and cross-linked to the activated thiol Sepharose 4B beads. The peptides were eluted with DTT and the free -SH groups blocked with IA then separated on FPLC. Two fractions contained [14C]MA. Sequence analyses showed that these labeled peptides contained Cys-51 and Cys-3734, respectively. Evidence suggests that the thiolester is formed between Cys-51 and gamma-Glu-54 for one, and Cys-3734 and beta-Asp-3737 for the other, with Lys and a hydrophobic amino acid, Val/Leu, in between. This is the first evidence for the presence of intramolecular thiolester linkages in ApoB. The presence of high energy, labile thiolester bonds may explain many of the unusual properties of ApoB and LDL.

Our studies of alpha-thrombin as a growth factor have led to the development of a synthetic peptide (p508) that in vitro competes with thrombin for binding to high affinity receptors, and enhances mitogenic activity. To determine if this peptide could be used to accelerate wound closure in vivo, full thickness 6 mm dermal biopsy wounds on the dorsal skin of anesthetized rats were treated with p508 peptide, thrombin or PBS as control. At day 7, the p508 treated wound areas were 20% to 50% smaller than either thrombin or PBS treated wound sites. This suggests that p508 enhances aspects of wound healing, and avoids the normal in vivo regulatory mechanisms of intact thrombin.

Hepatocytes were exposed in vitro to the hepatocarcinogen N-hydroxy-2-aminofluorene (N-OH-AAF) in order to determine the nature and repair of DNA adducts formed. N-OH-AAF formed 3 DNA adducts, N-(deoxyguanosin-8yl)-2-acetylaminofluorene (dG-C8-AAF), N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-C8-AF), and 3-(deoxyguanosin-N2-yl)-2-acetylaminofluorene (dG-N2-AAF). The removal of these adducts was measured up to 38 h following cessation of exposure to N-OH-AAF. The dG-C8-AAF adduct was removed with a half-life of about 10 h, while the other two remained relatively constant throughout the incubation period. The dG-C8-AAF adduct is probably responsible for the induction of unscheduled DNA synthesis (UDS) in this model in vitro system.

A cDNA encoding mouse tyrosinase was inserted into a plasmid containing the provirus of a replication competent Avian Leukosis Virus (ALV). A viral stock produced from the plasmid was used to infect cultured tyrosinase-negative (ca/ca) unpigmented chick embryo pigment cells. Five days after infection many cells were producing very dark discrete pigment granules. Cultures of tyrosinase positive, sex linked albino (sal) pigment cells produced no additional pigmentation. White Leghorn pigment cells responded to viral infection like the sal pigment cells.

Towards a goal of using adeno-associated viruses (AAV), the human parvovirus, as the gene transfer vector for gene therapy of hemoglobinopathies, the human beta-globin (h beta G) cDNA was ligated downstream of the P40 promoter of AAV type 2 (AAV2) genome. Transfection via electroporation of the construct into human 293 cells (embryonal kidney cell line) resulted in expression of the cloned h beta G cDNA, as evidenced by the synthesis of transcripts hybridizable to h beta G probe. The transfection led to the recombinant genome to be excised out of the plasmid and replicate in the cell, followed by production of the recombinant AAV that harbors h beta G cDNA.

The iron-binding plasma protein transferrin (TF) is essential for supplying iron to cells and the prevention of iron toxicity. Our laboratory has cloned and characterized the human TF gene. Comparison of promoter regions of TF genes from human, chicken, and mouse reveals a strong nucleotide sequence conservation. This study demonstrates that 5' flanking regions of the TF gene are sufficient for directing expression of a heterologous gene in transgenic mice and transfected cells. For cell-specific expression, more than 150 base pairs appear to be required.

We reported the construction of the structural gene for trans-activator (Tat) protein of human immunodeficiency virus. While maintaining the same amino acid sequence as the viral protein, the corresponding nucleotide sequence was modified to create additional recognition sites for restriction endonucleases and to prevent basepair mismatch during gene assembly. The oligonucleotides were synthesized chemically, purified and assembled into five gene blocks. The gene blocks were cloned into plasmid vectors and later reassembled into a complete gene. The use of gene blocks facilitated in vitro mutagenesis by the cassette mutagenesis method.