The nucleosome is generally found to be a strong barrier to transcript 
elongation by RNA polymerase II (pol II) in vitro. The elongation factors TFIIF 
and TFIIS have been shown to cooperate in maintaining pol II in the 
catalytically competent state on pure DNA templates. We now show that although 
TFIIF or TFIIS alone is modestly stimulatory for nucleosome traversal, both 
factors together increase transcription through nucleosomes in a synergistic 
manner. We also studied the effect of TFIIF and TFIIS on transcription of 
nucleosomes containing a Sin mutant histone. The Sin point mutations reduce 
critical histone-DNA contacts near the center of the nucleosome. Significantly, 
we found that nucleosomes with a Sin mutant histone are traversed to the same 
extent and at nearly the same rate as equivalent pure DNA templates if both 
TFIIS and TFIIF are present. Thus, the nucleosome is not necessarily an 
insurmountable barrier to transcript elongation by pol II. If unfolding of 
template DNA from the nucleosome surface is facilitated and the tendency of pol 
II to retreat from barriers is countered, transcription of nucleosomal templates 
can be rapid and efficient.