Differential expression of an hsp70 gene during transition from the mycelial to the infective yeast form of the human pathogenic fungus Paracoccidioides brasiliensis

We have isolated and characterized cDNA and genomic clones that encode a 70 kDa heat shock protein (Hsp70) from the dimorphic human pathogenic fungus Paracoccidioides brasiliensis, The gene encodes a 649-amino-acid protein sh owing high identity with other members of the hsp70 gene family. The hsp70 gene is induced during both heat shock of yeast cells at 42 degrees C and t he mycelial to yeast transition. A differential expression of this gene can be observed between mycelial and yeast forms, with a much higher level of expression in the yeast, We found two introns of 178 and 72 nucleotides in the P. brasiliensis hsp70 gene. Splicing of these introns is regulated duri ng the heat shock process and possibly during infection, In order to analys e the differential accumulation of unspliced mRNA following cellular differ entiation and/or heat shock, reverse transcriptase-polymerase chain reactio n (RT-PCR) experiments were carried out. The temperature-induced mycelial t o yeast transition results in the transient accumulation of unspliced hsp70 mRNA transcripts, Yeast cells, after adaptation at 36 degrees C, seem to b e more proficient at splicing, at least with respect to hsp70 mRNA because, during a severe heat shock (42 degrees C), the unspliced form of this mRNA does not accumulate. The mycelial to yeast differentiation will have the a daptational effect of increasing the resistance of the organism to environm ental stress, which may be necessary for parasite survival in the mammalian host.