Regulation of host RNA levels during baculovirus infection

During infection of the permissive host insect cell line Spodoptera frugiperda IPLB-SF-21 by the baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV), the levels of host actin, histone, and heat shock 70 (hsp70) RNAs are reduced substantially. Reduction of the host RNA levels occurs primarily during a narrow window of the replication process, from approximately 12 to 18 hr postinfection (p.i.), corresponding to the phase in which the extracellular form of the virus buds into the media. A late viral protein appears to be required for this reduction since cycloheximide, an inhibitor of cytosolic protein synthesis, and aphidicolin, an inhibitor of host and viral DNA polymerases, inhibit the reduction of actin and histone RNA levels. A cDNA corresponding to the carboxyl half of the S. frugiperda mitochondrial cytochrome c oxidase subunit III (COIII) gene was isolated, sequenced, and characterized. Two differentially regulated mitochondrial transcripts of this gene are observed. The level of the larger of these transcripts, which is dependent on active cytosolic protein synthesis, is reduced during virus infection in a fashion similar to that of the nuclear host genes. The smaller COIII transcript is stable until at least 24 hr p.i. but the level of this RNA eventually declines by 48 hr p.i.