Complete nucleotide sequence of an influenza virus haemagglutinin gene from cloned DNA

A synthetic fowl plague virus (FPV) haemagglutinin gene has been cloned in bacteria and the complete sequence of the RNA gene deduced. It is 1,742 nucleotides long and the mRNA codes for 56.3 amino acids in an uninterrupted sequence. The nature of some of the important domains in the haemagglutinin has been established, and their structure is discussed in relation to their function. Extensive amino acid sequence homologies exist between FPV and human influenza haemagglutinins.     

Complete nucleotide sequence of the AIDS virus, HTLV-III

The complete nucleotide sequence of two human T-cell leukaemia type III (HTLV-III) proviral DNAs each have four long open reading frames, the first two corresponding to the gag and pol genes. The fourth open reading frame encodes two functional polypeptides, a large precursor of the major envelope glycoprotein and a smaller protein derived from the 3'-terminus long open reading frame analogous to the long open reading frame (lor) product of HTLV-I and -II.     

Mouse p53 inhibits SV40 origin-dependent DNA replication

p53 is a cellular phosphoprotein that is present at elevated concentrations in cells transformed by different agents. p53 complementary DNA expression-constructs immortalize primary cells in vitro and co-operate with an activated ras oncogene in malignant transformation. Several reports have implicated p53 in mammalian cell cycle control and specifically with events occurring at the G0-G1 boundary. p53 forms specific complexes with simian virus 40 (SV40) large-T antigen, and such complexes are found associated with both replicating and mature SV40 DNA in lytically infected cells. In an accompanying paper Gannon and Lane report that in in vitro plate-binding assays, mouse p53 can displace polymerase alpha from complex with T-antigen. We have examined the in vivo consequences of expressing wild-type and mutant p53 proteins from other species in SV40-transformed monkey cells. We report here that expression of mouse p53 results in a substantial and selective inhibition of SV40 origin-dependent DNA replication. In addition to any function in the G0-G1 transition, the data presented suggest that p53 may affect directly the initiation or maintenance of replicative DNA synthesis.     

Phosphorylation of large tumour antigen by cdc2 stimulates SV40 DNA replication

Simian virus 40 large tumour antigen (T) is a replication origin binding protein required for viral DNA synthesis. Unphosphorylated T antigen is deficient in promoting DNA replication in vitro but can be activated by phosphorylation at residue threonine 124 by the cdc2 protein kinase. This observation demonstrates that T is regulated by phosphorylation and provides a model for cdc2 function in the control of DNA replication.     

Complete nucleotide sequence of bacteriophage MS2 RNA: primary and secondary structure of the replicase gene.

Bacteriophage MS2 RNA is 3,569 nucleotides long. The nucleotide sequence has been established for the third and last gene, which codes for the replicase protein. A secondary structure model has also been proposed. Biological properties, such as ribosome binding and codon interactions can now be discussed on a molecular basis. As the sequences for the other regions of this RNA have been published already, the complete, primary chemical structure of a viral genome has now been established.     

Elevated c-myc expression facilitates the replication of SV40 DNA in human lymphoma cells

The v-myc oncogene can induce tumours in haematopoietic, mesenchymal and epithelial tissues. The corresponding c-myc proto-oncogene can contribute to the genesis and/or the progression of an equally wide variety of tumours when activated by retroviral insertions, chromosomal translocations or gene amplification. The c-myc gene product is a DNA-binding, nuclear phosphoprotein that is involved in the control of cell proliferation and possibly in DNA synthesis. The replication of Simian virus 40 (SV40) is a useful model system to study eukaryotic DNA replication as the virus relies almost entirely on cellular DNA replication apparatus. The SV40-based vector, pSVEpR4, replicates poorly in the human BJAB lymphoma line and in most human cells, but replicates well in Burkitt lymphoma lines, which have fused immunoglobulin and c-myc genes, resulting in high c-myc expression. Cotransfection of the BJAB cells with a c-myc-expressing construct (pI4-P6) increased the replication of pSVEpR4 tenfold. Our findings indicate that overexpression of the c-myc gene product allows the replication of SV40 in human lymphoma cells, suggesting that c-myc is involved in the control of replication.     

p53 and DNA polymerase alpha compete for binding to SV40 T antigen

The large T antigen (T) of simian virus 40 is a multifunctional protein required for both viral DNA replication and cellular transformation. T antigen forms specific protein complexes with the host protein p53 in both virus-infected and transformed cells. p53 has recently been shown to be an oncogene, but its normal function is not clear. We previously established a radioimmunoassay to study the newly described complex between T antigen and DNA polymerase alpha, and have noted a similarity between the antigenic changes induced in T by the binding of both p53 and polymerase. We now extend this analysis to a larger collection of anti-T antibodies and formally establish that p53 and DNA polymerase alpha can compete for binding to the SV40 T antigen. At a critical concentration of the three components it is possible to detect a trimeric complex of T, p53 and DNA polymerase alpha. Our observations have important implications for the control by these nuclear oncogenes of viral and cellular DNA synthesis and viral host range in both normal and transformed cells. We present a model for the action of p53 in growth control.     

Yeast replication factor-A functions in the unwinding of the SV40 origin of DNA replication

Cell-free replication systems for simian virus 40 (SV40) DNA are taken to be a model for the replication of eukaryotic chromosomes, because only one viral protein is required to supplement the replication proteins provided by a human cell extract. To prove that these cellular proteins function in chromosomal DNA replication we have begun to identify homologous proteins in an organism that can be genetically manipulated. Here we report the identification of yeast replication factor-A (yRF-A) from Saccharomyces cerevisiae and show that it is functionally and structurally related to a human protein that is required for the initiation and elongation of SV40 DNA replication. Yeast RF-A, a multi-subunit phosphoprotein, is similar to the human protein in its chromatographic behaviour, subunit structure and DNA-binding activity. The yeast protein will fully substitute for the human protein in an early stage of the initiation of SV40 DNA replication. Substitution of yRF-A in the complete SV40 replication system, however, results in reduced DNA replication, presumably due to a requirement for species-specific interactions between yeast RF-A and the DNA polymerase complex.     

Defective repair of alkylated DNA by human tumour and SV40-transformed human cell strains

We have identified a group of 8 (among 39) human tumour cell strains deficient in the ability to support the growth of adenovirus 5 preparations treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), but able to support the growth of non-treated adenovirus normally. This deficient behaviour defines the Mer- phenotype. Strains having the Mer- phenotype were found to arise from tumours originating in four different organs. Relative to Mer+ strains, Mer- tumour strains showed greater sensitivity to MNNG-produced killing, greater MNNG-stimulated "DNA repair synthesis and a more rapid MNNG-produced decrease in semi-conservative DNA synthesis. Here we report that (1) Mer- strains are deficient in removing O6-methylguanine (O6-MeG) from their DNA after [Me-14C]MMNG treatment (Table 1); (2) Mer- tumour strains originate from tumours arising in patients having Mer+ normal fibroblasts (Fig. 1a, b); (3) SV40 transformation of (Mer+) human fibroblasts often converts them to Mer- strains (Fig. 1c, d); (4) MNNG produces more sister chromatid exchanges (SCEs) in Mer- than in Mer+ cell strains (Fig. 2).     

Complete nucleotide sequence of an immunoglobulin VH gene homologue from Caiman, a phylogenetically ancient reptile

Immunoglobulin variable (V) gene regions typify extensive multigenic families in terms of overall size, chromosomal arrangement and presence of large numbers of apparent pseudogenes. A unique mechanism of somatic reorganization involving recombination of VH, D and JH or VL and JL segments accompanies the differentiation of lymphoid cells and together with somatic mutation and other types of recombination accounts for V-region diversity. Although these processes have been well characterized in higher mammals, little is known concerning their origin and diversification during phylogenetic time. Previously, we described the blot-hybridization characteristics of murine VHIII probes with restriction enzyme-digested genomic DNA isolated from several phylogenetically critical species, including Caiman crocodylus, a modern representative of an ancient reptilian subclass. Here we have used a murine probe, S107V, to select homologous clones from a library of Caiman genomic DNA constructed in a lambda bacteriophage. The complete nucleotide sequence of a Caiman gene homologous to the murine VH gene and its adjacent 5' and 3' region is described. Comparison of the sequence with mammalian prototypes shows evidence of considerable organizational and structural homology extending outside the presumed VH-coding region and including elements believed to be involved in somatic recombination. Inferences about the evolution of this multigenic family can now be extended to the level of phylogenetic class.     

放线菌酮诱导SV40增强子的启动子活性的研究

在蛋白质合成抑制放线菌酮（CHX）诱导下,pCAT－E质粒中SV40增强子能启动CAT基因的表达,在很短的时间（5min)和很低的CHX质量浓度（30ng/mL）条件下,CHX即能诱导pCAT－E中SV40增强子的启动子活性,为了研究CHX诱导的pCAT-E质粒中SV40增强子的启动子活性是否与位置有关,构建了两个组体：pCAT-Bas-Enh(-)和pCAT-Bas-Enh( ),改变了SV40增强了序列与载体中CAT报告基因的相对位置,用重组质粒转染CHO细胞并用CHX处理,检测不到CAT活性,说明pCAT－E质粒中CHX所诱导的SV40增强子启动子活性受SV40增强子位置的影响。