7638
The CBC physically associates with these complexes to recruit them during transcription and mediates phosphorylation at Ser - 2 of the C - terminal domain ( CTD ) of RNA polymerase II .
 Chemical: Ser; Chemical: C
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: Ser; Chemical: C