Abstract: An extended species-specific sequence region of yeast transcription factor IIB (yTFIIB) (amino acids 144-157) is critical for cell viability and gene activation. Four residues in yTFIIB, Lys-147, Cys-149, Lys-151, and Glu-152, are critical for yeast cell growth. Intragenic suppressor experiments identified mutations that reversed, or partially reversed, the temperature sensitive phenotype of a yTFIIB derivative bearing amino acid changes at these four positions to human residues. Some of these residues (positions 115, 117 and 182) are located outside the species-specific region of yTFIIB. The identification of this species-specific region provides a unique and specific target for antifungal drugs and a screening assay therefor.