The SRB5 gene encoding the Med18 (Srb5) subunit of the Mediator complex of the Saccharomyces cerevisiae transcription apparatus was identified as a multicopy suppressor of the Leu111Ala (L111A) point mutation in the C-terminal region of the yeast RNA polymerase II subunit Rpb11. Thus, the functional interaction between one of the Mediator components and the core of the major transcription enzyme was shown for the first time. It is also important that the suppressed point mutation is located in the short C-terminal region of the Rpb11 subunit, which, as was demonstrated in our previous studies, has played an essential role in the evolution of the eukaryotic transcription machinery. © 2009 Pleiades Publishing, Ltd.