Cyclin (Bur2p)-dependent protein kinase%3B part of the BUR kinase complex which functions in transcriptional regulation%3B phosphorylates the carboxy-terminal domain (CTD) of Rpo21p and the C-terminal repeat domain of Spt5p%3B recruits Spt6p to the CTD at the onset of transcription%3B regulated by Cak1p%3B similar to metazoan CDK9 proteins