Major vault protein (MVP), is overexpressed in various multidrug-resistant cancer cell lines and clinical samples. The promoter of MVP is TATA-less; contains an inverted CCAAT-box and a Sp1 site located near a p53 binding motif. MVP has two alternative splice variants, which differ from each other within the 5'-leader. The long-MVP isoform is ubiquitously expressed and represents an almost constant portion of the total MVP mRNA in many different normal tissues. MVP is the major component of the multimeric ribonucleoprotein complexes, with several copies of an untranslated RNA, which has been shown to transport along cytoskeletal-based cellular tracks. In conclusion, MVP protein mediates drug resistance, perhaps via a transport process.