Heat shock response in Bombyx mori cells infected by nuclear polyhedrosis virus (NPV)

Silkworm (Bombyx mori) cells are characterized by the ability to synthesize heat shock proteins (hsps) at exceptionally high temperatures (up to 48° C). We infected B. mori larvae and tissue culture cells with the nuclear polyhedrosis virus (Mn NPV) and studied the heat shock response in the cells. Our results indicate that infected cells are not able to synthesize hsps after temperature elevation, polyhedrin (the major inclusion body protein of Mn NPV) being practically the only translational product in such cells. Similar results were obtained for infected fifth instar larvae of B. mori. On the other hand Northern hybridization experiments employing the Drosophila melanogaster hsp70 gene coupled with data on in vitro RNA transcription showed that temperature elevation induces active transcription of heat shock mRNAs in the infected cells. Therefore, the discrimination in favour of the viral mRNA for polyhedrin probably takes place at the level of translation.