Transcripts from the Drosophila heat-shock gene hsr-omega influence rates of protein synthesis but hardly affect resistance to heat knockdown

While hundreds of genes have recently been implicated in an organism s response to thermal stress, our insight into the cellular and physiological mechanisms affected by these genes has advanced to a lesser extent. We focus on an enigmatic Drosophila heat stress RNA gene, hsr-omega, which encodes two RNA transcripts that are constitutively expressed in almost all developing and adult tissues, omega-n in the nucleus and omega-c in the cytoplasm; both being readily induced to high levels by mild heat stress. We derived three hsr-omega mutant lines via imprecise P-element excision and characterised them for changes in expression, in both the presence and absence of heat stress. Viability estimates indicate that a low level of omega-n is required for normal development. Consistent with the model of omega-n as a negative regulator of intron-processed mRNA levels the mutants displayed a 1.5-fold increase in rates of protein synthesis measured in ovarian tissue in the absence of heat stress, a result suggesting that an important function of hsr-omega is the modulation of general protein synthesis. The mutants had little effect on two measures commonly used to assess heat tolerance, heat-knockdown time and heat hardening ability, suggesting that more subtle heat-related fitness components need to be examined for effects of these mutations.