A POINT MUTATION IN THE GENE ENCODING THE RUBISCO LARGE SUBUNIT INTERFERES WITH HOLOENZYME ASSEMBLY

Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), a key enzym e of photosynthetic CO, fixation, is composed of 8 large and 8 small s ubunits. The Rubisco-deficient Nicotiana tabacum mutant Sp25 is able t o synthesize the peptides for both subunits but does not contain any a ctive holoenzyme. The phenotype is maternally inherited and thus cause d by a mutation in the chloroplast genome, which also encodes the Rubi sco large subunit. A comparison of the nucleotide sequences of the lar ge subunit gene of the Sp25 mutant with that of the wild-type tobacco revealed a single nucleotide change in the Sp25 mutant, This resulted in an amino acid substitution at Gly-322, which was replaced by serine .