Three alleles of rbsB gene including export defective mutant were cloned for overproduction of proteins. Five different species of precursor and mature ribose-binding proteins were purified to homogeneity. The purified proteins were subjected to amino acid sequencing. The results confirmed the amino acid changes deduced from the DNA sequencing (Park et al., 1988a). Attempts were made to establish a correlation between export competency and conformation of the proteins by studies in vitro. In this regard, ligand binding ability, circular dichroism, and the sensitivity to the degradation by a protease were compared. However, there was no drastic conformational difference among these proteins in steady states. This results, in other aspect, implied that the proteins purified from the overproduced proteins are in native conformation and allowed further analysis for studying the mechanism of protein export in vitro.