A reporter gene was constructed of the Chlamydomonas reinhardtii rbcL 5 f region from position -70 to +47, relative to the transcription start point (+1), followed by the E. coli uidA (GUS) gene and the Chlamydomonas psaB 3 f region downstream of it. Two constructs were made in order to examine the importance of the sequence of a predicted stem-loop structure between positions +1 and +41 of the C. reinhardtii rbcL 5 e region. The first construct tested consisted of a reversed nucleotide sequence between positions +5 and +37, while the second construct examined consisted of a complete change of sequence between positions +6 and +36 of the region, in which the nucleotides were changed so that each purine is replaced by another purine (A ¨G; G ¨A), and each pyrimidine by another pyrimidine (C ¨T; T ¨C).The constructs were inserted into the chloroplast genome downstream of the atpB gene. Transcript accumulation of the reporter gene was determined by Northern blot. Both constructs did not exhibit a change in accumulation of GUS transcripts in comparison to the original reporter gene construct, proving that the altered nucleotides are not significant in stabilizing the rbcL transcript in the C. reinhardtii chloroplast.