Molecular basis of the ribulose-1,5-bisphosphate carboxylase/oxygenase activase mutation in Arabidopsis thaliana is a guanine-to-adenine transition at the 5'-splice junction of intron 3.

Analysis of the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase gene and gene products from Arabidopsis thaliana wild-type plants and the Rubisco activase-deficient mutant strain showed that the rca mutation caused GT to be changed to AT at the 5'-splice junction of intron 3 in the six-intron pre-mRNA. Northern blot analysis, genomic and cDNA sequencing, and primer extension analysis indicated that the mutation causes inefficient and incomplete splicing of the pre-mRNA, resulting in the accumulation of three aberrant mRNAs. One mutant mRNA was identical with wild-type mRNA except that it included intron 3, a second mRNA comprised intron 3 and exons 4 through 7, and the third mRNA contained exons 1 through 3. The G-to-A transition is consistent with the known mechanism of mutagenesis by ethyl methanesulfonate, the mutagen used to create the Rubisco activase-deficient strain.