Transcription termination can easily be described as a cessation of RNA synthesis and DNA dissociation. All genes utilizing Pol II have a post-modification signal for the poly A tail and that sequence is AAUAAA.  The AAUAAA sequence is usually position about 10 – 50 nucleotides upstream of a GU-rich downstream sequence element [10].   It is the appearance of this poly A tail that causes cessation of Pol II.  There has been evidence that Pol II  CTD promotes proper cleavage and  that the Pol II-associated terminus is a substrate for the 5’ to 3’ exoribonuclease Xrn2.  However, the appearnce of TFIIS also promotes cleavage. Exoribonuclease Xrn2 is then thought to terminate transcription upon cessation of Pol II by cleaving the transcript [11]. A different study supported this explaination for termination in yeast cells. They found that an endonuclease Rat1 also terminated transcription utilizing the same mechanism [12]. After cleavage a long poly A tail is added. With the presence of the CAP and Poly A tail, the mRNA is now ready for splicing ending termination and transcription.