The present invention relates to a polynucleotide comprising a ubiquitous chromatin opening element (UCOE) which is not derived from 13. The polynucleotide of any one of claims 1 to 7, wherein the UCOE comprises the sequence of FIG. 20 between nucleotides 1 to 7627 or a functional homologue or fragment thereof. an LCR. The present invention also relates to a vector comprising the polynucleotide sequence, a host cell comprising the vector, use of the polynucleotide, vector or host cell in therapy and in an assay, and a method of identifying UCOEs. The UCOE opens chromatin or maintains chromatin in an open state and facilitates reproducible expression of an operably-linked gene in cells of at least two different tissue types.