N-terminal deletion in the src gene of Rous sarcoma virus results in synthesis of a 45,000-Mr protein with mitogenic activity.

Expression of the v-src gene of Rous sarcoma virus in avian embryo neuroretina cells results in transformation and sustained proliferation of these normally resting cells. Transformed neuroretina cells are also tumorigenic upon inoculation into immunodeficient hosts. We have previously described conditional mutants of Rous sarcoma virus encoding p60v-src proteins which induce proliferation of neuroretina cells in the absence of transformation and tumorigenicity. These results suggest that p60v-src is composed of functionally distinct domains which may interact with multiple cellular targets. In this study, we describe a spontaneous variant of Rous sarcoma virus, subgroup E, which carries a deletion of 278 base pairs in the 5' portion of the v-src gene but which has retained the ability to induce proliferation of quail neuroretina cells. The deleted v-src gene encodes a 45,000-molecular-weight phosphoprotein which contains both phosphoserine and phosphotyrosine, is myristylated, and possesses tyrosine kinase activity indistinguishable from that of wild-type p60v-src. Molecular cloning and sequence analysis of the mutant v-src gene have shown that this deletion extends from amino acid 33 to 126 of the wild-type p60v-src. Therefore, this portion of the v-src protein is dispensable for the mitogenic activity of Rous sarcoma virus in neuroretina cells.     

Growth of B95-8 cells and expression of Epstein-Barr virus lytic phase in serum-free medium.

Epstein-Barr virus (EBV)-transformed tamarin (Saguinus oedipus) cells (B95-8) were selected for growth in medium with reduced serum and then transferred to serum-free medium which consisted of RPMI 1640 supplemented with insulin, transferrin, and selenium. Serum-free cells in continuous passage for 1 year had a morphology, growth rate, and culture density which approached those of B95-8 cells grown with serum. The cells expressed virus-induced antigens, including the EBV-associated DNA polymerase. Cells exposed to EBV-inducing agents, n-butyric acid and phorbol 12-myristate-13-acetate, produced transforming virus with titers comparable to those of cultures grown with serum. These findings demonstrate that serum is neither required for the growth of B95-8 cells nor necessary for induction or full expression of the EBV lytic phase in these cells.     

Integration of hepatitis B virus: analysis of unoccupied sites.

Hepatitis B virus (HBV) sequences integrated in the PLC/PRF/5 cell line (Alexander cells), which was derived from a human primary liver carcinoma, were previously extensively studied. Here we describe the analysis of the unoccupied sites of two linearly integrated forms of HBV DNA, AL-14 and AL-26, that were characterized previously. No major cellular DNA rearrangements were seen at the integration sites except for small deletions of host sequences: 2 kilobases of DNA in AL-14 and 17 base pairs (bp) in AL-26. The unoccupied site of AL-26 was found to be missing 182 bp, which previously mapped next to the right end of the integration sites of several independent clones. These were believed to be of cellular origin, but we show here that these 182 bp are in fact from unusual HBV sequences. Surprisingly, a region of this newly detected HBV DNA sequence is more homologous to that of woodchuck HBV DNA. Our analysis shows that the normal counterparts of both AL-14 and AL-26 contain minisatellite-like repetitive sequences. Based on the data presented here and our previous finding of HBV DNA integration at satellite sequences, we propose that genomic simple repetitive sequences are hot spots for HBV DNA integration.     

Structure and expression of the herpes simplex virus type 2 glycoprotein gB gene.

The gene for glycoprotein gB2 of herpes simplex virus type 2 strain 333 was cloned, sequenced, and expressed in mammalian cells. The gB2 protein had an overall nucleotide and amino acid sequence homology of 86% with the cognate gB1 protein. However, of the 125 amino acid substitutions or deletions, only 12.5% were conservative replacements. These differences were clustered within an NH2-terminal region, a central region, and a COOH-terminal region, resulting in domains of near identity broken by small regions of marked divergence. Regions of greatest homology included a 90-amino-acid stretch starting at residue 484 and 39 amino acids spanning residues 835 to 873, which cover a rate-of-entry locus mapped to Ala-552 and a syn locus mapped to Arg-857, respectively, in gB1 by Bzik et al. (D. J. Bzik, B. A. Fox, N. A. DeLuca, and S. Person, Virology 133:301-314, 1984). Pellett et al. (P. E. Pellett, K. G. Kousoulas, L. Pereira, and B. Roizman, J. Virol. 53:243-253, 1985) mapped the mutations in three monoclonal antibody-resistant gB1 mutants between amino acids 273 and 443. These epitopes are included in a region of 98 residues identical between gB1 and gB2. The identity of this protein was verified by placing a truncated gene lacking the 303 carboxyl-terminal amino acids of gB2 into mammalian COS and CHO cells. Expression was demonstrated by immunofluorescence and radioimmunoprecipitation. This protein will be purified from the stable CHO cell lines and compared with gB1 for immunogenicity and protective efficacy in animal challenge models.     

Human immunodeficiency virus neutralizing antibodies recognize several conserved domains on the envelope glycoproteins.

Serum neutralizing antibodies against the human immunodeficiency virus were frequently detected in infected individuals, and low or absent serum neutralizing titers correlated with poor prognosis. Multiple diverse human immunodeficiency virus isolates were found to exhibit similar susceptibility to neutralization by a panel of human seropositive sera, suggesting that neutralizing antibodies are largely directed against conserved viral domains. Furthermore, utilizing antisera raised against a library of synthetic env peptides, four regions which are important in the neutralization process have been identified within both human immunodeficiency virus envelope glycoproteins (gp41 and gp120). Three of these are in conserved domains and should be considered for inclusion in a candidate vaccine.     

Two of the three influenza viral polymerase proteins expressed by using baculovirus vectors form a complex in insect cells.

Each of the influenza virus polymerase (P) genes PB1, PB2, and PA was inserted into a baculovirus vector under the control of the polyhedrin promoter. In insect (Spodoptera frugiperda) cells infected by each baculovirus recombinant containing a P gene insert, a large amount of the encoded P protein was synthesized. Gel electrophoretic analysis of the total proteins in infected cells revealed the presence of a new protein band corresponding to the encoded P protein that was abundant enough to be stained with Coomassie blue. In cells infected simultaneously with both the PB1 and PB2 baculovirus recombinants, a PB1-PB2 complex was formed that was immunoprecipitated with an antiserum specific for either PB1 or PB2. In cells infected simultaneously with all three P baculovirus recombinants, a PB1-PB2 complex lacking the PA protein was formed. Formation of this PB1-PB2 complex partially mimics events that occur in influenza virus-infected cells, where all three P proteins form a complex with each other (B. M. Detjen, C. St. Angelo, M. G. Katze, and R. M. Krug, J. Virol. 61:16-22, 1987). These results indicate that the ability of PB1 and PB2 to form a complex is an intrinsic property of these two proteins that does not require the participation of other influenza viral gene products. Possible reasons for the absence of the PA protein from the immunoprecipitable P protein complex in insect cells infected by the three P baculovirus recombinants are discussed.