RNA polymerase I holoenzyme-promoter complexes include an associated CK2-like protein kinase

In eukaryotes, RNA polymerase I (pol I) transcribes the tandemly repeated g enes that encode the precursor of 18S, 5.8S and 25S ribosomal RNAs. In plan ts and animals, the pol I enzyme can be purified in a holoenzyme form that is self-sufficient for promoter binding and accurate, promoter-dependent tr anscription in a cell-free system. In this report, we show that a casein ki nase 2 (CK2)-like protein kinase co-purifies with pol I holoenzyme activity purified from broccoli (Brassica oleracea). Using an immobilized template assay, we show that the CK2-like activity is part of the protein-DNA comple x that results upon binding of the holoenzyme to the rRNA gene promoter. Th e CK2 activity phosphorylates a similar set of holoenzyme proteins both bef ore and after promoter binding. These data provide further evidence that po l I holoenzyme activity can be attributed to a single, multi-protein comple x self-sufficient for promoter association and accurate, promoter-dependent transcription.