Cell line-specific accumulation of the baculovirus non-hr origin of DNA replication in infected insect cells

Successive viral passage of Spodoptera exigua multicapsid nucleopolyhedrovirus (SeMNPV) in the S. exigua cell line Se301 leads to the rapid accumulation of the non-hr origin of DNA replication (ori) as large concatemers. Passage of SeMNPV in two other S. exigua cell lines, SeUCR1 and SeIZD2109, did not show the accumulation of such concatemers. When introduced into SeUCR1 and SeIZD2109 cells, the non-hr ori concatemers generated in Se301 cells were maintained but did not increase. This suggests that the non-hr ori confers a strong selective advantage in Se301 cells, but not or to a lesser extent in the other cell lines. The cell line-specific accumulation of non-hr ori concatemers might be due to a higher intrinsic recombination frequency in Se301 cells and may reflect tissue related differences involving some host cell factor(s). Since non-hr ori concatemers in Se301 cells were more abundant in intracellular than in extracellular viral DNA preparations, episomal replication and the requirement of a minimal DNA size for packaging into nucleocapsids is hypothesized.