In order to discover novel factors involved in elongation by RNA
polymerase II (RNAPII), several subunits of S. cerevisiae RNAPII were
TAP-tagged and purified. One novel factor identified by mass
spectrometry that co-purified with RNAPII is the previously
uncharacterized ORF, Ydl115c, which we have named Iwr1 (interacts with
RNA polymerase II). When Iwr1 was tagged and purified, it co-purified
with a nearly stoichiometric amount of transcriptionally active RNAPII.
An iwr1 deletion strain is sensitive to 6-azauracil, suggesting Iwr1
could have a role in transcriptional elongation. In synthetic genetic
array (SGA) analysis, an iwr1 deletion was found to genetically interact
with several known elongation factors, including TFIIS and components of
the Paf1 complex, with mediator subunits Gal11 and Soh1, and with
components of the Set1 and Set3 complexes. Interestingly, iwr1 also
results in synthetic lethality when combined with a deletion of RPB9, a
subunit of RNAPII previously implicated in transcriptional elongation.
Finally, antibody was generated against the D. melanogaster homologue of
Iwr1. dIwr1 localizes to actively transcribed regions on polytene
chromosomes: it co-localizes with RNAPII phosphorylated on Ser2 of the
CTD, a form of polymerase known to be involved in transcriptional
elongation. Our combined data suggest that Iwr1 is an evolutionarily
conserved protein which functions in transcriptional elongation.