Molecular cloning, transcriptional characterization, and sequencing of cDNA encoding the H-protein of the mitochondrial glycine decarboxylase complex in peas

Abstract

The glycine decarboxylase multienzyme complex is located in the mitochondrial matrix and catalyzes a key reaction of the photorespiratory C-2 cycle of C3 plants. The cDNA encoding the smallest subunit, the 13,900-dalton H-protein, of the glycine decarboxylase complex from pea (Pisum sativum) leaves was cloned, identified, characterized, and sequenced. The 678-nucleotide sequence contained a 495-nucleotide open reading frame capable of encoding the 165-amino-acid H-protein precursor. The N terminus of this protein contains a 34-amino-acid sequence which does not appear in the mature protein. This presequence resembles the amphiphilic helices observed with mitochondrial leader sequences in yeast. The 131-amino-acid mature protein from peas shares substantial homology with the enzyme isolated from chicken liver. The abundance of the H-protein mRNA was about 5-fold greater in light-grown pea seedlings compared to dark-grown seedlings. The amount of H-protein transcript increased within 4 h after the plants were transferred to white light and continued to increase up to 24 h. The time course for the accumulation of the H-protein mRNA was similar to that for the mRNA of the small subunit of ribulose-1,5-bisphosphate carboxylase.