Cloning of the gene (gdcH) encoding H-protein, a component of the glycine decarboxylase complex of pea (Pisum sativum L.).

H-protein is the lipoyl-protein component of the glycine decarboxylase complex, which catalyses, with serine hydroxymethyltransferase, the mitochondrial step of photorespiration in plants. We have isolated and characterized the gene (gdcH) encoding the H-protein in pea (Pisum sativum L.). The H-protein gene is distributed in a stretch of about 1.55 kbp and contains three introns (75, 64 and 185 bp) located in the coding region. No intervening sequences were detected in the 5' and 3' non-coding regions. This intron-exon structure contrasts with the preliminary H-protein gene structures reported for human and chicken, where these genes (dispersed on 13 and 8 kbp genomic fragments respectively) are composed of five highly conserved exons and are interrupted by four long introns. Two main transcription sites were detected by primer extension of RNA. The first transcriptional initiation site was assigned the +1 position and correlated with a putative TATA box located at position -26. The second transcriptional start site was not correlated with a putative TATA box, but may be regulated by an 'initiator' element described by Smale & Baltimore [(1989) Cell (Cambridge, Mass.) 57, 103-113] which contains, within itself, the transcription start site. The presence of two potential promoters may be related to the specialized overexpression pattern of H-protein in leaves, in order to support photorespiration.