Comparison of sequence diversity in several cytoplasmic polyhedrosis viruses

Lipofectin increases the specific activity of cypovirus particles for cultured insect cells

Cytoplasmic polyhedrosis viruses (CPV) are classified as 14 distinct species (electropherotypes) within the genus Cypovirus, family Reoviridae. Cypovirus research has been limited by a lack of appropriate cell culture systems (for each of these virus species) in which the majority of cells can become productively infected. Lipofection increased the infection rate of Lymantria dispar 652 cells, by virus particles (derived from polyhedra) of Orgyia pseudosugata type 5 cypovirus (Op-5 CPV), from 3 to 44%. Lipofection also significantly increased the percentage of Trichoplusia ni 368 cells infected with the same virus (from < 1 to approximately 7%). The spread of cypovirus infection between cells was either very slow or insignificant, and infected cells appeared to remain viable for long periods. Virus infection was detected by the observation of polyhedra formation in individual cells and it was therefore possible to develop a simple quantitative assay system to measure virus titre (TCID50). Cryo-electron microscopy showed that cypovirus particles formed a complex with the lipid, involving their envelopment within the liposome membrane. It was concluded that the increased infectivity of the virus by lipofection was due to a more efficient cell entry mechanism, probably involving fusion between liposome and cell membranes.

Sequence analysis and expression of the polyhedrin gene of Choristoneura fumiferana cytoplasmic polyhedrosis virus (CfCPV)

The segmented double-stranded RNA genome of Choristoneura fumiferana cytoplasmic polyhedrosis virus (CfCPV) was extracted, polyadenylated, reverse-transcribed into cDNA and cloned. The cDNA clones that hybridized to the smallest genomic segment (segment 10) were identified, and its nucleotide sequence was determined. Genome segment 10 of CfCPV was found to be 1171 nucleotides in length with a single open reading frame in one strand capable of coding a predicted protein of 258 residues (Mr of 29,795), consistent with an apparent Mr of 30.5 kDa determined by SDS-PAGE of purified polyhedrin. Comparison of the nucleotide and amino acid sequences of the polyhedrin gene of CfCPV with those of other CPVs and with several nuclear polyhedrosis viruses revealed no particular homology. Analysis of the hydrophilic profiles and predicted secondary structures of Bombyx mori (BmCPV), Euxoa scandens (EsCPV) and CfCPV indicated the presence of seven similar regions located at the amino terminus of the polyhedrin polypeptide of the three viruses. The expression of the cloned CfCPV polyhedrin gene in Escherichia coli demonstrated that this polyhedrin has the property of self-assembly, since the production of crystal-like occlusion with a well-defined crystalline lattice structure was observed.

RNA editing in the phosphoprotein gene of the human parainfluenza virus type 3

RNA editing of the human parainfluenza virus type 3 (HPIV3) phosphoprotein (P) gene was found to occur for the accession of an alternate discontinuous cistron. Editing occurred within a purine-rich sequence (AAUUAAAAAAGGGGG) found at the mRNA nucleotides 791-805. This sequence resembles an HPIV3 consensus transcription termination sequence and is located at the 5'-end of the putative D protein coding sequences. Editing at an alternate site (AAUUGGAAAGGAAAGG), mRNA nucleotides 1121-1136, for accession of a conserved V cistron, which is present in a number of paramyxovirus P genes, was not found to occur in HPIV3. In contrast with many other paramyxoviruses, editing was indiscriminate with the insertion of 1-12 additional G residues not present in the gene template. RNA editing was found to occur in both in vivo (HPIV3 infected cells) and in vitro (purified nucleocapsid complexes) synthesized mRNAs. Further, the in vitro prepared mRNA was edited regardless of whether the nucleocapsid complexes were transcribed in the presence or absence of uninfected human lung carcinoma (HLC) cell lysates. These results support the notion that RNA editing appears to be exclusively a function of viral proteins.

Nucleotide sequence of the polyhedrin gene of Euxoa scandens cytoplasmic polyhedrosis virus (EsCPV)

The double-stranded RNA genome of Euxoa scandens cytoplasmic polyhedrosis virus (EsCPV) was reversely transcribed to the double-stranded DNA and cloned into pIBI30. The complete nucleotide sequence of cloned genome segment 10, which encodes the virus polyhedrin polypeptide, was determined. The EsCPV polyhedrin gene consists of 881 bp and possesses an open reading frame that codes for a polypeptide of 269 amino acids (MW 30.1K), consistent with an apparent MW of 30K determined by SDS-PAGE for purified polyhedrin. The sequence is identical to that reported for the amino terminus of polyhedrin from the CPV of Orgyia pseudotsugata; however, no amino acid or nucleotide sequence homology was found between the EsCPV polyhedrin and that from Bombyx mori CPV (BmCPV) or several nuclear polyhedrosis viruses. The hydrophilic profiles and predicted secondary structures of both EsCPV and BmCPV polyhedrin show some similarities, mainly in the amino half of the polypeptides. These data should be helpful in identifying the domains responsible for the polyhedrin crystallizing properties.

Physical Analysis of the Campoletis sonorensis Virus Multipartite Genome and Identification of a Family of Tandemly Repeated Elements

This report is an analysis of cross-hybridizing sequences found within the 28 superhelical (SH) DNAs of the multipartite genome of the polydnavirus Campoletis sonorensis virus (CsV). A Southern cross-blot hybridization analysis showed that the majority of CsV Eco RI restriction fragments cross-hybridize to multiple Eco RI fragments. These sequence homologies were analyzed by hybridizing recombinant clones of the CsV SH DNAs B, H, M, and O 1 to Southern blots of undigested CsV DNA, using different hybridization stringencies. The results indicated that homologous regions among the SH DNAs include closely related sequences that are detectable under stringent conditions and related but more diverged sequences which are only detectable under reduced stringencies. A sequence that hybridized to the majority of the CsV SH DNAs was identified and subcloned from the SH DNAs O 1 , H, and B. Nucleotide sequence data revealed that these homologous regions contained a family of imperfectly conserved repeated elements. These repeat elements were arranged singly or in direct tandem arrays and had an average length of 540 base pairs. Within the sequenced regions that contained the repeated elements six putative open reading frames were identified. These results show that the CsV genome consists of SH DNAs with complex sequence interrelationships that may have arisen due to multiple recombinational events.

Molecular cloning and sequence analysis of the human parainfluenza 3 virus RNA encoding the nucleocapsid protein

The sequence of 1690 nucleotides from the 5' end of the viral complementary RNA for the human parainfluenza 3 virus was determined by molecular cloning. One large open reading frame consisting of 1548 nucleotides was demonstrated. The encoded protein, the nucleocapsid protein (NP), consists of 515 amino acids, and has a predicted molecular weight of 57,819. A noncoding 5' sequence of 51 nucleotides is present at the end of the NP-mRNA. Two consensus sequences were identified which are homologous with sequences found in Sendai virus. One of these sequences, AGGATTAAAG, was located at the 5' end of the nucleocapsid mRNA and may function in transcription initiation. The other consensus sequence, GTAAGGGAA, was found in the viral genomic leader sequence. The nucleocapsid protein amino acid sequence was compared to other members of the Paramyxoviridae family. The parainfluenza 3 virus protein nucleocapsid amino acid sequence demonstrated a high degree of homology with the Sendai virus nucleocapsid protein. Seventy percent of the first 387 amino acids from the amino termini were identical. Little homology was observed in the distal carboxy termini.

Assessment of sequence relatedness of double-stranded RNA genes by RNA-RNA blot hybridization

Three well-characterized reovirus serotypes were used to investigate the usefulness of RNA-RNA blot hybridization as a means to assess the genetic relatedness of double-stranded RNA (dsRNA) viruses. [5'-32P]pCp-labeled genomic dsRNAs from reovirus 1, 2 and 3 were used as probes in hybridization experiments in which segments of the three serotypes were separated in 10% polyacrylamide gels and transferred electrophoretically to membranes. Nine of the 10 reovirus genes cross-hybridized between the serotypes. The S1 gene was serotype specific. The L2 gene of reovirus 2 showed a lower level of cross-hybridization with types 1 and 3 when compared to the hybridization signal observed for L2 when types 1 and 3 were hybridized to each other. The data were consistent with previous studies on the relatedness of the three virus serotypes. Since RNA-RNA blot hybridization allows the number and identity of conserved genes to be determined, this approach may prove useful for assessing the genetic relatedness among other viruses in the family Reoviridae.