CLONING AND ANALYSIS OF AN ACTIN-ENCODING CDNA FROM THE DIMORPHIC PATHOGENIC FUNGUS HISTOPLASMA-CAPSULATUM

We have cloned an actin-encoding cDNA from the dimorphic fungus Histop lasma capsulatum, an important pathogen of humans. The predicted amino acid sequence as well as the general codon pattern of Histoplasma act in revealed the highest degree of similarity to the actin of the filam entous ascomycete Aspergillus nidulans. Southern blot analysis determi ned that actin was encoded by a single copy in the Histoplasma?a genom e. Northern blot analysis showed a single 1700 nt transcript in yeast and mould cells as well as in cells undergoing the temperature induced mould-to-yeast conversion. Actin mRNA levels normalized to 18 S rRNA were found to be equivalent in all the stages examined, except for a s harp four-fold transient decrease 4 h into the mould-to-yeast conversi on. These data suggest that actin mRNA would not be a suitable interna l marker for expression studies during Histoplasma mould-to-yeast morp hogenesis.