The eukaryotic transcript elongation factor TFIIS is encoded by a nonessential 
gene, PPR2, in Saccharomyces cerevisiae. Disruptions of PPR2 are lethal in 
conjunction with a disruption in the nonessential gene TAF14/TFG3. While 
investigating which of the Taf14p-containing complexes may be responsible for 
the synthetic lethality between ppr2Delta and taf14Delta, we discovered genetic 
interactions between PPR2 and both TFG1 and TFG2 encoding the two larger 
subunits of the TFIIF complex that also contains Taf14p. Mutant alleles of tfg1 
or tfg2 that render cells cold sensitive have improved growth at low temperature 
in the absence of TFIIS. Remarkably, the amino-terminal 130 amino acids of 
TFIIS, which are dispensable for the known in vitro and in vivo activities of 
TFIIS, are required to complement the lethality in taf14Delta ppr2Delta cells. 
Analyses of deletion and chimeric gene constructs of PPR2 implicate 
contributions by different regions of this N-terminal domain. No strong common 
phenotypes were identified for the ppr2Delta and taf14Delta strains, implying 
that the proteins are not functionally redundant. Instead, the absence of Taf14p 
in the cell appears to create a dependence on an undefined function of TFIIS 
mediated by its N-terminal region. This region of TFIIS is also at least in part 
responsible for the deleterious effect of TFIIS on tfg1 or tfg2 cold-sensitive 
cells. Together, these results suggest a physiologically relevant functional 
connection between TFIIS and TFIIF.