HIGH CONSTITUTIVE LEVELS OF HEAT-SHOCK PROTEINS IN HUMAN-PATHOGENIC PARASITES OF THE GENUS LEISHMANIA

We have analysed the transcription of three heat-shock genes, HSP70, H SP83 and ClpB, in the protozoan parasite Leishmania. All three heat-sh ock genes are transcribed constitutively and not heat-inducibly. Howev er, we find that two major heat-shock proteins, HSP70 and HSP83, are s ynthesized at elevated rates during heat stress. We conclude that the cellular stress response in Leishmaniae is regulated exclusively on a post-transcriptional level much in contrast with all other eukaryotes examined so far. The induced synthesis of HSP70 and HSP83, however, do es not increase the steady-state level of either protein significantly . This is compensated by high constitutive levels of both proteins: HS P70 and HSP83, however, does not increase the steady-state level of ei ther protein significantly. This is compensated by high constitutive l evels of both proteins: HSP70 and HSP83 make up 2.1% and 2.8%, respect ively, of the total protein in unstressed Leishmania promastigotes. Al so, HSP70 is a strictly cytoplasmic protein in Leishmania and does not relocate into the nucleus during heat stress, as it does in other euk aryotes examined in the past.