A gene coding for the subunit B (GapB) of chloroplast glyceraldehyde-3-phosphate dehydrogenase fi om spinach and its two derivatives (GapBc) lacking the GapB-specific C-terminal extension have been cloned by RT-PCR, These three genes have been overexpressed with full activity in Escherichia coli when a two-cistron expression system controlled by an inducible promoter P,, is used. With a suitable base composition of the first cistron, the expression level of GapB and the derivatives GapBc are expressed up to 15-20% of the total cell protein and around 20 mg of recombinant GapBcs with full activity are purified from 1 liter of cultured bacteria. The specific activity of the two derivatives GapBc (40-60 u/mg) is similar to that of GapA (50-70 u/mg) and lower than that of reported GapBc derivative (E, Baalmann, R, Scheibe, R. Cerff, and W. Martin, 1996, Plant Mol. Biol. 32, 505-513).