To understand the mechanism of protein export in general and to identify conponent(s) of export machinery utilized by ribose-binding protein, we examined the effects of three prlA suppressors on the export of an export-defective mutant rbsB103. We also studied the requirement(s) of SecY protein and leader peptidase on the export of wide-type ribose-binding protein. The export defect of rbsB103 mutation was not suppressed by three prlA alleles tested. However, SecY protein appears to affect for the export of wide-type ribose-binding protein. Wild-type precursor ribose-binding protein was not processed by purified leader peptidase(lep product) in vitro.