CLONING AND CHARACTERIZATION OF A NOVEL P-GLYCOPROTEIN HOMOLOG FROM BARLEY

P-glycoproteins are members of a large superfamily of transport protei ns (the 'traffic ATPases') that utilize ATP to translocate a wide rang e of substrates across biological membranes. Using a PCR-based approac h, and degenerate oligonucleotides corresponding to conserved motifs, two 300-bp cDNA fragments (pBMDR1 and pBMDR2) with a significant seque nce similarity to mammalian P-glycoproteins were amplified from barley (Hordeum vulgare) root poly A(+) RNA and used as probes to screen a b arley root cDNA library. A single full-length clone pHVMDR2 coding for a polypeptide of 1232 residues (c. 134 kDa) was isolated. Comparison of this barley sequence with Arabidopsis ATPGP1 and human MDR1 and MDR 3 P-glycoprotein sequences showed that the barley cDNA has 44%, 37% an d 38% amino acid (aa) identity, respectively, with these sequences, an d conserved structural features. RNase protection analysis showed that HVMDR2 mRNA is expressed at low levels in both barley roots and leave s. Southern blot analyses indicated that there is a small multigene fa mily related to P-glycoproteins in barley. Possible functions for thes e barley P-glycoproteins are discussed. (C) 1997 Elsevier Science B.V.