Structural organization and splice variants of the POLE1 gene encoding thecatalytic subunit of human DNA polymerase epsilon

The catalytic subunit of human DNA polymerase epsilon, an enzyme involved i n nuclear DNA replication and repair, is encoded by the POLE1 gene. This ge ne is composed of 51 exons spanning at least 97 kb of genomic DNA. It was f ound to encode three alternative mRNA splice variants that differ in their 5'-terminal sequences and in the N-termini of the predicted proteins. A CpG island covers the promoter region for the major transcript in HeLa cells. This promoter is TATA-less and contains several putative binding sites for transcription factors typical of S-phase-up-regulated and serum-responsive promoters. Potential promoter regions were also identified for the two othe r alternative transcripts. Interestingly, no nuclear polyadenylation signal sequence was detected in the 3'-untranslated region, although a poly(A) ta il was present. These results suggest a complicated regulatory machinery fo r the expression of the human POLE1 gene, including three alternative trans cripts expressed from three promoters.