Auxin-binding protein located in the endoplasmic reticulum of maize shoots: molecular cloning and complete primary structure.

We previously purified an auxin-binding protein (ABP) from the microsomal fraction of maize shoots (Zea mays L. cv. Golden Cross Bantam). In the present study cDNA clones derived from mRNAs encoding the ABP were isolated and sequenced. The nucleotide sequence of the 822-base-pair cDNA includes a 603-base-pair open reading frame. RNA blot hybridization analysis indicated a single mRNA species of approximately 1.0 kilobase. The predicted precursor of ABP is composed of 201 amino acid residues and has a molecular weight of 21,976. The NH2-terminal sequence of 38 residues is hydrophobic and may be a signal peptide for translocation of the ABP across the membrane of the endoplasmic reticulum. The mature ABP, composed of 163 residues with a molecular weight of 18,352, contains a potential N-glycosylation site (Asn-Thr-Thr), and the COOH-terminal tetrapeptide (Lys-Asp-Glu-Leu) may be a signal for retention of the ABP in the lumen of the endoplasmic reticulum.