STRUCTURE OF THE CAC1 GENE AND IN-SITU CHARACTERIZATION OF ITS EXPRESSION - THE ARABIDOPSIS-THALIANA GENE CODING FOR THE BIOTIN-CONTAINING SUBUNIT OF THE PLASTIDIC ACETYL-COENZYME-A CARBOXYLASE

The CAC1 gene of Arabidopsis thaliana that codes for the biotin carbox yl-carrier subunit of the heteromeric acetyl-coenzyme A carboxylase wa s isolated and sequenced. CAC1 is a single-copy gene interrupted by si x introns. Subcellular immunogold labeling indicates that the biotin c arboxyl-carrier subunit is localized in the stroma of the plastids and chloroplasts. The CAC1 mRNA accumulates throughout developing embryos and ovules of siliques at a time of rapid growth and oil accumulation (7 d after flowering), but is present at much lower levels in wall ce lls and central septal cells of the silique. Immunolocalization studie s show that the pattern of accumulation of the biotin carboxyl-carrier subunit within the siliques and leaves is similar to that of the CAC1 mRNA. These observations indicate that the cellular pattern of biotin carboxyl-carrier protein accumulation in the developing silique may b e determined by the transcriptional activity of the CAC1 gene.