C-terminal domains of general regulatory factors Abf1p and Rap1p in Saccharomyces cerevisiae display functional similarity.

Abf1p and Rap1p are global regulatory factors which play an essential role in the transcription activation of yeast ribosomal protein genes. This functional link prompted us to investigate whether these factors may be functionally interchangeable. We focused on the indispensable C-terminal portions of both factors and performed mutual domain swaps. The functional capacity of the resulting hybrid proteins was subsequently examined using yeast strains conditionally expressing either the ABF1 or the RAP1 gene. Both the Abf1p-Rap1p and the Rap1p-Abf1p fusion proteins were found to be able to complement the growth defect of the respective strains. Furthermore, Abf1p and Rap1p are both able to promote transcription of a reporter gene through a combination of the respective binding site and a T-rich promoter element. These data strongly suggest that the C-terminal domains of Abf1p and Rap1p have, at least partially, identical functions. Finally, a deletion analysis of the so far largely uncharacterized C-terminal domain of Abf1p was performed, which revealed that two regions of 50 amino acids can perform all essential Abf1p functions.