Woodchuck Hepatitis Virus (WHP) Posttranscriptional Regulatory Element (WPRE) is a DNA sequence that, when transcribed creates a tertiary structure enhancing expression. Commonly used in molecular biology to increase expression of genes delivered by viral vectors.  WPRE is a tripartite regulatory element with gamma, alpha, and beta components. The alpha component is 80bp long:

GCCACGGCGGAACTCATCGCCGCCTGCCTTGCCCGCTGCTGGACAGGGGCTCGGCTGTTGGGCACTGACAATTCCGTGGT

When used alone without the gamma and beta WPRE components the alpha component is only 9% as active as the full tripartite WPRE. The sequence for full tripartite WPRE is as foollows.
TCGACAATCAACCTCTGGATTACAAAATTTGTGAAAGATTGACTGGTATTCTTAACTATGTTGCTCCTTTTACGCTATGTGGATACGCTGCTTTAATGCCTTTGTA
TCATGCTATTGCTTCCCGTATGGCTTTCATTTTCTCCTCCTTGTATAAATCCTGGTTGCTGTCTCTTTATGAGGAGTTGTGGCCCGTTGTCAGGCAACGTGGCGTG
GTGTGCACTGTGTTTGCTGACGCAACCCCCACTGGTTGGGGCATTGCCACCACCTGTCAGCTCCTTTCCGGGACTTTCGCTTTCCCCCTCCCTATTGCCACGGCGG
AACTCATCGCCGCCTGCCTTGCCCGCTGCTGGACAGGGGCTCGGCTGTTGGGCACTGACAATTCCGTGGTGTTGTCGGGGAAGCTGACGTCCTTTCCATGGCTGCT
CGCCTGTGTTGCCACCTGGATTCTGCGCGGGACGTCCTTCTGCTACGTCCCTTCGGCCCTCAATCCAGCGGACCTTCCTTCCCGCGGCCTGCTGCCGGCTCTGCGG
CCTCTTCCGCGTCTTCGCCTTCGCCCTCAGACGAGTCGGATCTCCCTTTGGGCCGCCTCCCCGCCTG

This sequence has 100% homology with base pairs 1093 to 1684 of the Woodchuck hepatitis B virus (WHV8) genome. When used in the 3′ UTR of a mammalian expression cassette it can significantly increase mRNA stability and protein yield.