No abstract

In late 2005, sporadic cases of an acute onset disease of high mortality were observed in 10- to 16-week-old growing pigs among several swine herds of the United States. Tissues from the affected pigs in Kansas, Iowa, and North Carolina were examined, and porcine circovirus type 2 (PCV2) was detected consistently among these tissues. Phylogenetically, PCV2 can be divided into two major genotypic groups, PCV2-group 1 and PCV2-group 2. Whereas PCV2-group 1 isolates were detected in all the diseased animals, only two of the diseased animals harbored PCV2-group 2 isolates. This observation is important because PCV2-group 1 isolates had never been reported in the United States before (GenBank as of May 16, 2006), and they are closely related to the PCV2-group 1 isolates that have been described in Europe and Asia, previously. Our analysis revealed that each genotypic group contains a distinct stretch of nucleotide or amino acid sequence that may serve as a signature motif for PCV2-group 1 or PCV2-group 2 isolates.

Porcine circovirus type 2 (PCV2) is the causative agent of an emerging swine disease, postweaning multisystemic wasting syndrome. In this work, the RNAs of PCV2 synthesized during productive infection in porcine kidney cells were characterized. A total of nine RNAs were detected. They include the viral capsid protein RNA (CR), a cluster of five Rep-associated RNAs (designated Rep, Rep', Rep3a, Rep3b, and Rep3c), and three NS-associated RNA (designated NS515, NS672, and NS0). Members of the Rep-associated RNA cluster all share common 5' and 3' nucleotide sequences and they also share 200 common 3' nucleotides with the NS-associated RNAs. Rep, capable of coding for the replication-associated-protein (RepP), appears to be the primary transcript that gives rise to Rep', Rep3a, Rep3b, and Rep3c by alternate splicing. Protein sequence alignment showed that RepP and the Rep' protein of PCV2 are equivalent to those described for PCV type 1 (PCV1) (a nonpathogenic virus), which had been shown to be essential for viral DNA replication. The results also suggest that NS515, NS672, and NS0 are transcribed from three different promoters inside ORF1 downstream of the Rep promoter. To date, only three RNAs (CR, Rep, and Rep') have been reported for PCV1-infected porcine kidney cells. Therefore, it is important to apply similar strategies from this study to reexamine the transcription pattern of PCV1.

No abstract

A clone of human cells (Detroit 6) latently infected by adeno-associated virus (AAV) has been characterized with regard to the status of the viral DNA. In both early (9 to 10) and late (118) passages of the clone, AAV-DNA was recombined with host DNA, at least in some cases as a head-to-tail tandem repeat, via the terminal sequences of the viral genome. However, it was not possible to distinguish between integration into chromosomal DNA and very large plasmids (< 20 x 10(6) molecular weight) which contain both viral and cellular DNA sequences. Although evidence for some modifications of the viral sequence was obtained, most of the integrated sequences appeared to be intact. In some cases sequences of undetermined origin separated adjacent copies of the viral genome. Free copies of the AAV genome were detectable in late passage cells, but not in early passage cells. The orientation of nucleotide sequences present in the free AAV DNA from late passage cells was indistinguishable from that of virion DNA. With the notable exception, the organization of the integrated AAV sequences as determined by restriction enzyme digestion remained constant with continued passage. Digestion with SmaI, which cleaves within the palindromic region of the terminal repetition in AAV DNA, produced reproducibly different patterns when early and late passage DNAs were compared. Several models for rescue of free copies of the genome from the integrated DNA are possible, all of which involve the terminal repetition.

At least three separate regions of the Epstein-Barr virus (EBV) genome encode RNA in a cell line that is growth transformed and nonpermissively infected with EBV. Six polyadenylylated cytoplasmic RNAs have been identified from these three regions. An abundant RNA 3.0-3.1 kilobases (kb) long is encoded by DNA of the internal reiteration, IR, and DNA that maps at 25.7-30 megadaltons. A second, abundant, 2.9-kb RNA is primarily encoded by DNA at 110-03 megadaltons but probably has a 3' end to the left of 110 megadaltons. A third, abundant, 3.7-kb RNA is largely encoded by DNA at 63-66 megadaltons and has a 5' end to the left of 63 megadaltons. A less-abundant 1.5-kb RNA is also encoded by IR. The least-abundant polyadenylylated RNAs identified are 2.3 and 2.0 kb. These RNAs have 3' ends mapping of 5-7 megadaltons and 5' ends mapping to the right of 7 megadaltons. The data suggest that there may be two additional polyadenylylated cytoplasmic RNAs, a 3-kb RNA mapping at 26.2-30 megadaltons and a minor RNA mapping at 102-110 megadaltons. An abundant 0.16-kb nonpolyadenylylated RNA is also present in the cytoplasm of IB-4 cells. This RNA precipitates from the cytoplasm in the presence of high concentrations of magnesium, indicating that it is complexed with protein or polyribosomes.

A novel porcine parvovirus, PPV4, was identified in the lung lavage of a diseased pig coinfected with porcine circovirus type 2. This virus exhibits limited similarity to its closest relative, bovine parvovirus 2, but resembles viruses of the genus Bocavirus (bovine parvovirus, canine minute virus and human bocavirus) that encode an additional ORF3. The ORF3 of PPV4 is predicted to encode a protein of 204 amino acid residues, which is similar in size to the ORF3-encoded proteins of the bocaviruses. Whereas the ORF3-encoded proteins of bocaviruses share significant similarity with each other, the PPV4 ORF3 encoded protein does not exhibit homology with any protein in the GenBank non-redundant database.

The genome and transcriptional pattern of a newly identified respiratory variant of transmissible gastroenteritis virus were analyzed and compared with those of classical enterotropic transmissible gastroenteritis virus. The transcriptional patterns of the two viruses indicated that differences occurred in RNAs 1 and 2(S) and that RNA 3 was absent in the porcine respiratory coronavirus (PRCV) variant. The smaller RNA 2(S) of PRCV was due to a 681-nucleotide (nt) deletion after base 62 of the PRCV peplomer or spike (S) gene. The PRCV S gene still retained information for the 16-amino-acid signal peptide and the first 6 amino acid residues at the N terminus of the mature S protein, but the adjacent 227 residues were deleted. Two additional deletions (3 and 5 nt) were detected in the PRCV genome downstream of the S gene. The 3-nt deletion occurred in a noncoding region; however, the 5-nt deletion shortened the potential open reading frame A polypeptide from 72 to 53 amino acid residues. Significantly, a C-to-T substitution was detected in the last base position of the transcription recognition sequence upstream of open reading frame A, which rendered RNA 3 nondetectable in PRCV-infected cell cultures.