Analysis of the intron-exon organization of the human multidrug-resistance protein gene (MRP) and alternative splicing of its mRNA

Overexpression of multidrug-resistance protein (MRP) and P-glycoprotein confers similar but not identical multidrug-resistance phenotypes. However, unlike P-glycoprotein, which comprises two membrane-spanning domains (MSDs) and two nucleotide-binding domains, MRP contains a third NH2-proximal MSD, a feature now identified in several other ATP-binding cassette transmembrane transporters. MRP is located on chromosome 16 at band 13.1 close to the short-arm breakpoint of the pericentric inversion associated with the M4Eo subclass of acute myeloid leukemia. We have defined the intron-exon structure of MRP and characterized a number of splicing variants of MRP mRNA. The gene spans at least 200 kb, It contains 31 exons and a high proportion of class 0 introns, alternative splicing of which results in significant levels of variant transcripts that maintain the original open reading frame of MRP mRNA. Analyses of the conservation of intron-exon organization and protein primary structure suggest that the MRP-related transporters evolved from a common ancestor shared with the cystic fibrosis transmembrane conductance regulator, by fusion with one or more genes encoding polytopic membrane proteins. (C) 1997 Academic Press.