Physical and Functional Interaction between Elongator and the Chromatin-associated Kti12 Protein

Cells lacking KTI12 or Elongator (ELP) genes are insensitive to the toxin zymocin and also share more general phenotypes. Moreover, data from low stringency immunoprecipitation experiments suggest that Elongator and Kti12 may interact. However, the precise relationship between these factors has not been determined. Here we use a variety of approaches to investigate the possibility that Elongator and Kti12 functionally overlap. Native Kti12 purified to virtual homogeneity under stringent conditions is a single polypeptide, but depletion of Kti12 from a yeast extract results in co-depletion of Elongator, indicating that these factors do interact. Indeed, biochemical evidence suggests that Elongator and Kti12 form a fragile complex under physiological salt conditions. Purified Kti12 does not affect Elongator histone acetyltransferase activity in vitro. However, a variety of genetic experiments comparing the effects of mutation in ELP3 and KTI12 alone and in combination with other transcription factor mutations clearly demonstrate a significant functional overlap between Elongator and Kti12 in vivo. Intriguingly, chromatin immunoprecipitation experiments show that Kti12 is associated with chromatin throughout the genome, even in non-transcribed regions and in the absence of Elongator. Conversely, RNA-immunoprecipitation experiments indicate that Kti12 only plays a minor role for Elongator association with active genes. Together, these experiments indicate a close physical and functional relationship between Elongator and the highly conserved Kti12 protein.