CTD Ser5 phosphorylation by CDK7/Kin28 allows promoter escape and enables pausing.
Dephosphorylation of CTD Ser5 involves several phosphatases.
CDK12 likely has specialized, cell type-specific and/or gene-specific roles in human.
CTD Tyr1 phosphorylation has different distribution patterns, and most likely different functions, in yeast and metazoans.
Some RNA processing factors feedback on CTD phosphorylation.