Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 14, 2012
Publication Date: October 26, 2012
Citation: Cheung, A.K. 2012. Replicative intermediates of porcine circovirus in animal tissue cultured cells or in bacteria undergoing copy-release replication. Virology. 434(1):38-42. Interpretive Summary: In 2004, a swine disease with a sudden onset of high mortality in 10- to 16-week-old pigs in Eastern Canada was recognized in numerous herds. This syndrome was first observed in the United States in mid 2005 in North Carolina and quickly spread throughout the United States within a year. Porcine circovirus type 2 (PCV2) was soon identified as the cause of this postweaning multisystemic wasting syndrome (PMWS) in swine, and more recently as the etiological agent of a collection of disease syndromes labeled Porcine Circovirus Associated Disease (PCVAD). Although vaccines are now available, PCVAD remains an important viral pathogen of swine and understanding the biology of this virus will provide clues into how this virus emerged as a pathogen as well as potential improvements in the management of PCVAD. Previously, we identified several genetic differences between PCV2 and the non-pathogenic PCV1, and determined essential and non-essential genetic elements required for the replication of these two viruses. Here we report detection of previously unrecognized intermediates in the replication cycle of PCV2. The information obtained advances our understanding of circovirus biology and aids the research of scientists in industry, universities and government agencies.
Technical Abstract: Porcine circovirus (PCV) has been assumed to replicate its genome via the rolling-circle replication (RCR) mechanism because it encodes a Rep protein that contains several amino acid motifs commonly found in other RCR biological systems. Two proteins, Rep and Rep', are essential for PCV DNA replication in mammalian cells. In this work, replicative intermediates of PCV-infected porcine kidney (PK15) cells or copy-release of PCV genomes from a head-to-tail tandem construct (without Rep') in Escherichia coli were examined. In PK15 cells, replicative intermediates consistent with complementary-strand replication which converts single-stranded circular genome to double-stranded supercoiled DNA and RCR which generates single-stranded plus strand progeny genome were observed. To a lesser extent, intermediates suggestive of recombination-dependent replication were also detected. In Escherichia coli, copy release of the single-stranded circular PCV genome with conversion to a supercoiled molecule by complementary-strand synthesis was observed. However, replicative intermediates indicative of RCR were not detected.