Investigating the Effects of Sumoylation on the Yeast General Transcription Factor TFIIF

Sumoylation is a post-translational modification that regulates numerous cellular processes including gene expression. We find that among the general transcription factors of RNA Polymerase II (RNAPII) in budding yeast, transcription factor IIF (TFIIF) shows a relatively high level of sumoylation, primarily on Lysine residues (Lys) 60/61 of its Tfg1 subunit. Fractionation analysis indicates that sumoylated Tfg1 is associated with chromatin, but its sumoylation level is not affected by stresses. Although Lys 60/61 were previously implicated in the Tfg1-RNAPII interaction, a Lysine-to-Arginine K60,61R mutation, which dramatically reduces Tfg1 sumoylation, does not affect that interaction. Chromatin immunoprecipitation analyses did not conclusively determine whether reducing Tfg1 sumoylation affects the recruitment of TFIIF or RNAPII to target gene promoters, but the expression of some genes is elevated in yeast expressing the K60,61R mutation. Our results demonstrate that chromatin-associated TFIIF is constitutively sumoylated which might be necessary for controlling the expression levels of some genes.