Tobacco (20) to give pl9S-C (Fig. 1A).An 850-bp Sac I-EcoRV fragment from pUC-19S-CAT, comprising the CAT sequence and the 3' proximal 65 bp of the 19S promoter sequence (including all 12 bp of the 19S 5' untranslated region), was cloned in the antisense orientation next to the nos 3' region in a pUC18 derivative to give pACN9. A 1.95-kilobase (kb) Pvu II fragment from pAGS120 (21) containing a chimeric HPT gene was inserted downstream from the antisense CAT-nos 3' sequence in pACN9.The rbcS promoter (-1040 to + 169) from Nicotiana plumbaginifolia, isolated as a 1.2-kb EcoRI-Pvu II fragment from pNPSS8B (a gift from N.-H. Chua), was cloned into the EcoRI and Sma I sites of pBinl9 to give pBrbcS. A 3.3-kb Xba 1-HindlIl fragment containing the antisense CAT-nos 3' fusion and the chimeric HPT gene was cloned into Xba I-and HindIII-linearized pBrbcS to give pRAC-H (Fig. 1B).An EcoRI-blunted HindIII fragment from pUC13/35SCAT (22) containing the CaMV 35S promoter (-941 to + 9) was cloned into the EcoRI and Sma I sites of Bluescript M13+ (Stratagene, San Diego) to give pBS-35S. A 1300-bp Xba IHincII fragment from pACN9 containing the antisense CATnos 3' sequence was cloned into the Xba I and blunted Sac II sites of pBS-35S to give pBS-35S-AC. The HPT coding sequence, isolated as a 1070-bp Xho II fragment from pAGS120, was inserted between the 35S promoter and antisense CAT-nos 3' sequence of pBS-35S-AC to give