Inhibition of the induction of heat shock proteins in Drosophila melanogaster cells infected with insect picornaviruses

Infection of cells by mammalian picornaviruses results in an inhibition of ‘shut-off’ of host cell protein synthesis to varying extents depending upon the virus used [ 11. The recently characterised picornaviruses of insects have been shown to act similarly, with Cricket paralysis virus (CrPV) being extremely efficient in inhibitingDrosophila cell protein synthesis [2,3], whereas the related Drosophila C virus (DCV) is relatively inefficient [4]. Effort has been concentrated on the elucidation of the shut-off mechanisms although this has not led to a satisfactory model being established. Work has been hindered by having to look at the inhibition of a broad spectrum of cellular proteins and also by the absence of a method to differentiate between the effects on mRNA existing before infection and de novo expression of genes during the course of infection. This means that while theories of shut-off at the level of translation may serve to explain events occuring early in the infection process, they may not necessarily be valid models for later shut-off. To overcome both these problems, we have utilised the phenomenon of heat-shock in Drosophila in which elevated temperature induces the expression of a novel set of genes. This was first recognised in vivo as a new puffing pattern in Drosophila melanogaster salivary gland chromosomes and has since been demonstrated in many of the tissues of this fly, as well as in Drosophila tissue culture cells [S]. Elevation of the temperature of Drosophila tissue culture cells shifts the pattern of protein synthesis from a normal broad spectrum of proteins to a small number of previously unexpressed proteins. This makes it possible to examine the effect of infection on a small number of proteins which are synthesised at a known chromosomal site