Sequence comparison of cellular and viral copies of host cell DNA insertions found in Autographa californica nuclear...

The nucleotide sequence and structural characteristics of two nonhomologous host DNA insertions of Spodoptera frugiperda (fall armyworm) origin isolated from few polyhedra mutants of the baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV) have been determined. Neither of the host insertions contain long open reading frames suggesting that cellular genes were not introduced into the viral genome. One of the host DNA insertions, IFP1.6, terminated in short imperfect inverted repeats flanked by a duplication of the target sequence, TTAA. Analysis of three cellular copies of this host insertion isolated from a lambda genomic library of S. frugiperda DNA revealed the termini to be highly conserved and also flanked by the same TTAA sequence. IFP1.6 was shown to share homology with a putative host insertion described in the genome of a baculovirus exhibiting wild-type plaque morphology. The second of the host insertions, IFP2.2, had a structure unique among host insertions described in baculoviruses. It lacks terminal repeats but is flanked by duplications of the 8-bp target site sequence. The cellular copy of this insertion was conserved in comparison to the viral copy and was also flanked by a direct 8-bp repeat. This is the first report of the analysis of cellular copies of host DNA insertions frequently associated with baculovirus FP mutants.