Figure 2. Model illustrating transcription at point and regional centromeres. In S. cerevisiae, the length of the CEN3 sequence is only 117 bp and contains three DNA elements, CDEI, CDEII and CDEIII. The transcription factor Cbf1 binds the CEN3 CDEI site, and Ste12 binds a site pericentromeric of CEN3. RNA Polymerase II (RNAP II) is required for centromeric transcription regulated by Cbf1 and Ste12. Antagonists such as silencing factors might contribute to transcriptional regulation. In S. pombe, the length of the cen1 sequence is 35 kb, and includes a central core (cnt) of non-repetitive sequence and inner (imr) and outer (comprising dg and dh repeats) repeats. RNA Pol II is required for pericentromeric transcription regulated by opposing activities of Clr3 (histone deacetylase, HDAC) and Epe1 (transcriptional activator). The balance of the antagonists determines the functional status at the pericentromeric heterochromatin. Centromeric transcripts are degraded by RNAi machinery and exosomes. The red bar represents the proposed transcriptional levels at repetitive and non-repetitive sequences of the centromere.