Expression of alpha tubulin during the dimorphic transition of Paracoccidioides brasiliensis

The actin gene in Paracoccidioides brasiliensis: organization, expression and phylogenetic analyses

PbrACT1, the gene responsible for the synthesis of actin in Paracoccidioides brasiliensis, was found as a single copy, organized into six exons and five introns. Its open reading frame (ORF) codes for a putative protein of 375 amino acids, with a molecular mass of 41.5 kDa and an isoelectric point of 5.6. Analysis of the nucleotide sequence revealed a high homology to other fungal actins, the presence of characteristic fungal actin sequences, and heat shock elements at the 5' untranslated region (UTR). Phylogenetic analyses with deduced amino acid sequences of fungal actins grouped P. brasiliensis within the phylum Ascomycota, order Onygenales, in concordance with a few previous reports. Patterns of expression through the temperature-induced morphological transitions from mycelial to yeast-like shapes and reverse, suggests that PbrACT1 is regulated in this process. The PbrACT1 gene sequence is available at the GenBank database under accession number AY383732.

Differential expression of actin modulated by temperature in mycelial and yeast cells of Paracoccidioides brasiliensis

We used yeast and mycelial forms of Paracoccidioides brasiliensis to evaluate the effect of heat shock stress on actin expression. P. brasiliensis yeasts harvested during the exponential growth phase showed more expression of the actin mRNA when incubated at 40 degrees C than when incubated at 37 degrees C, the usual temperature at which these yeasts grow. In contrast, expression of actin mRNA was lower in yeasts incubated at 25 degrees C than in yeasts incubated at 37 degrees C. Mycelium harvested at 25 degrees C, an approximation of its normal growth temperature, and then exposed to 37 degrees C and 40 degrees C showed progressively higher expression of actin mRNA. Mycelial and yeast forms showed a similar pattern of response to exposure to supra-optimal temperatures: both showed the same increase in expression of actin. This suggests that actin may play a role not only in cellular differentiation but also in this species' rapid adaptive response to heat stress, a mechanism necessary to deal with a potentially hostile environment.