Human adenovirus type 5 variants with sequence alterations flanking the E2A gene: effects on E2 expression and DNA replication

The human adenovirus type 5 (Ad5) E2 transcription unit is divided into a promoter-proximal region, E2A, and a distal region, E2B, each with its own polyadenylation site. Together these regions encode the three virus-derived proteins necessary for genome replication. Ad5 variants were produced that carried linker insertion mutations immediately 5' and/or 3' to the coding sequence for the E2A gene DNA binding protein (DBP). Two variants carrying solely a 5' lesion showed decreased usage of the adjacent 3' splice site, via which the DBP mRNA is produced, and an increased usage of the alternative downstream splice sites in the E2B region, wherein viral DNA polymerase and terminal protein precursor are encoded; these viruses showed somewhat reduced growth. A variant carrying a 3' lesion showed a marginal increase in DBP expression and slightly accelerated growth. When lesions 5' and 3' to the DBP coding sequence were combined in cis, the resulting virus was severely defective for growth and expressed E2B products to the virtual exclusion of E2A DBP. These data indicate that interactions must occur between the E2A 3' splice site and polyadenylation site before this region can be treated as an exon by the RNA processing machinery, and that a sequence alteration at the polyadenylation site that alone has only minor effects on the pattern of RNA processing can drastically affect terminal exon usage when placed in cis with a mutation that reduces splicing efficiency at the upstream 3' splice site. The data further indicate that, in vivo, Ad5 DNA replication is limited by prevailing DBP levels rather than by levels of polymerase or terminal protein precursor.

Constitutive episomal expression of polypeptide IX (pIX) in a 293-based cell line complements the deficiency of pIX mutant adenovirus type 5

The human adenovirus type 5 capsid is composed of a number of distinct polypeptides. It has been shown previously that one of these, polypeptide IX (pIX), is not absolutely required for the production of viable virus. However, viruses lacking this polypeptide have a significantly reduced packaging limit and, in the one case studied, also show a thermolabile virion phenotype. This report describes the use of eukaryotic episomal vectors based on the Epstein-Barr virus replicon to generate cells which stably express pIX. These cells provide pIX that is efficiently incorporated into virions that are genetically pIX-; such enhanced thermostability. These cells have also been used to isolate a genetically pIX- virus having a genome of length some 2.3 kbp in excess of the previously defined packaging limit for pIX- virus; the resulting virions have wild-type thermostability. These cells expand the theoretical capacity of adenovirus vectors for foreign DNA to around 9.2 kbp and may therefore be useful in gene therapy applications in which vector capacity is limiting.

Human adenovirus type 5 recombinants expressing simian immunodeficiency virus macaque strain gag antigens

The p55 gag gene of simian immunodeficiency virus macaque strain (SIVmac) and the core p27 gag component linked to a synthetic AUG codon have been cloned into adenovirus type 5 vectors to generate either viable E3-replacement or defective E1-replacement viruses. The viruses express the expected SIV proteins in both human and, for the non-defective viruses, monkey cells. A considerable proportion of the p55 produced is exported from the infected cell. These viruses should prove useful both in studies of the immune response to SIV and as components of candidate vaccines aimed specifically at provoking cytotoxic T cell responses.

Assignment of mutant tsN19 (complementation group E) of respiratory syncytial virus to the P protein gene

The mutation responsible for the temperature-sensitive (ts) phenotype of mutant tsN19 (complementation group E) of respiratory syncytial virus has been located to the P protein gene. Viral protein synthesis was completely restricted at 39 degrees C, and the tsN19 P protein did not react with an anti-P monoclonal antibody (MAb) (3-5) at 33 degrees C. Reversion of temperature sensitivity restored reactivity with MAb 3-5. Nucleotide sequence determination and in vitro expression of cDNA clones of P mRNA derived from wild-type, tsN19 and non-ts revertant-infected cells, revealed that temperature sensitivity and loss of reactivity with MAb 3-5 were consequences of a Gly----Ser amino acid change at position 172. A low M(r) polypeptide, which represented the C-terminal 93 amino acids of the P protein, was produced by internal initiation in the P open reading frame during in vitro translation, and a similar product was detected transiently in vivo.

Effect of changes in the nucleotide sequence of the P gene of respiratory syncytial virus on the electrophoretic mobility of the P protein

A consensus sequence for the P protein gene of the RSN-2 strain of respiratory syncytial (RS) virus was obtained by PCR amplification of cDNA obtained by reverse transcription. This established that the extent of sequence variation between two P genes of strains of antigenic subtype B is similar to that among A strains, confirming the conservation of P genes within subtypes and the divergence of the two antigenic subtypes of RS virus. The P protein of RS virus exhibits anomalous electrophoretic mobility with respect to its molecular weight. In vitro transcription and translation of RSN-2 strain cDNA possessing single point mutations revealed that substitutions involving charged amino acids in the carboxy-terminal region had a marked effect on the electrophoretic mobility of the P protein.

Defective synthesis of envelope proteins by temperature-sensitive mutants representing complementation groups B and D of respiratory syncytial virus

The phenotypes of two complementing temperature-sensitive (ts) mutants of respiratory syncytial (RS) virus indicate that the mutational lesions involve the attachment (G) and matrix (M) proteins of the viral envelope. Synthesis of the G protein was affected in cells infected with mutant tsA2 (complementation group B); the p50 precursor of the G protein was synthesized normally, but further maturation to the fully glycosylated form was defective at 39 degrees C. A non-ts alteration in the efficiency of cleavage of the F0 precursor to the F1 and F2 subunits of the fusion protein was also observed in tsA2-infected cells, which is consistent with the aberrant non-syncytial plaque morphology induced by tsA2 in certain cells. In cells infected with mutant tsN1 (complementation group D) the M protein disappeared from the soluble cytoplasmic fraction soon after synthesis at 39 degrees C and had a slightly decreased electrophoretic mobility. The M protein of non-ts revertants was stable at 39 degrees C, which links the defect in M protein stability with the tsN1 phenotype. However, the aberrant mobility phenotype remained, suggesting pseudoreversion. These results assign two of the eight complementation groups of ts mutants of RS virus.