TFIIB is essential for transcription initiation by RNA polymerase II. TFIIB also 
cross-links to terminator regions and is required for gene loops that juxtapose 
promoter-terminator elements in a transcription-dependent manner. The 
Saccharomyces cerevisiae sua7-1 mutation encodes an altered form of TFIIB (E62K) 
that is defective for both start site selection and gene looping. Here we report 
the isolation of an ssl2 mutant, encoding an altered form of TFIIH, as a 
suppressor of the cold-sensitive growth defect of the sua7-1 mutation. Ssl2 
(Rad25) is orthologous to human XPB and is a member of the SF2 family of 
ATP-dependent DNA helicases. The ssl2 suppressor allele encodes an arginine 
replacement of the conserved histidine residue (H508R) located within the 
DEVH-containing helicase domain. In addition to suppressing the TFIIB E62K 
growth defect, Ssl2 H508R partially restores both normal start site selection 
and gene looping. Moreover, Ssl2, like TFIIB, associates with promoter and 
terminator regions, and the diminished association of TFIIB E62K with the PMA1 
terminator is restored by the Ssl2 H508R suppressor. These results define a 
novel, functional interaction between TFIIB and Ssl2 that affects start site 
selection and gene looping.