RBP (ribose-binding protein) is a periplasmic protein responsible for ribose chemotaxis and ribose transport in E.coli. It is synthesized as a precursor form, exported into the periplasm and processed into mature form. Physical properties of precursor RBP and mature RBP were compared in this study. Tryptic digestion and molecular weight analysis of digested fragment showed that precursor RBP has a conformation which is resistant to proteolytic enzyme except for the signal sequence. CD spectra and ANS-binding properties showed that precursor RBP has a conformation very similar to that of mature RBP with no exposed hydrophobic region. Signal sequence in precursor RBP appears to contribute to the more efficient binding of precursor RBP to membrane vesicles than mature RBP. It seems that electrostatic and hydrophobic interaction of signal sequence with membrane lipid is important in the export pathway.