The human mdr1 (multidrug-resistance) gene harbours a long homopyrimidine.homopurine sequence next to a cluster of Alu repeated sequences in intron 14.

In order to identify specific DNA sequences useful as 'genetic landmarks' in the construction of a complete map of the human mdr1 (multidrug-resistance) gene, we investigated the introns in the central region. In intron 14, we identified a long stretch of a homopyrimidine.homopurine sequence most probably adopting an unconventional DNA conformation, followed by a cluster of three Alu repeated sequences in an inverted orientation. Here, we describe the structure, formation and nucleotide sequence of these DNA elements.