Structure of the PCCA gene and distribution of mutations causing propionicacidemia

Propionyl-CoA carboxylase (PCC, EC 6.4.1.3) is a mitochondrial, biotin-depe ndent enzyme that functions in the catabolism of branched-chain amino acids , fatty acids with odd-numbered chain lengths, and other metabolites. It ca talyzes the ATP-dependent carboxylation of propionyl-CoA to D-methylmalonyl -CoA. PCC is composed of two types of subunits, likely as alpha (4)beta (4) or alpha (6)beta (6), with the a subunit containing the covalently bound b iotin prosthetic group. A genetic deficiency of PCC activity causes propion ic acidemia, a potentially fatal disease with onset in severe cases in the newborn period. Affected patients may have mutations of either the PCCA or PCCB gene. In this study, we have determined the structure of the human PCC A gene which, at the present time, is only partially represented in the dat abases. Based on reported ESTs and confirmed by RT-PCR, we also redefine th e translation initiation codon to a position 75 nucleotides upstream of the currently accepted initiation codon. We show the distribution of mutations , including three identified in this study, and renumber all reported mutat ions to count from the new initiation codon. The gene spans more than 360 k b and consists of 24 exons ranging from 37 to 335 bp in length. The introns range in size from 104.bp to 66 kb. We have also determined the nucleotide sequence of similar to1 kb of the 5'-flanking region upstream of the ATG t ranslation initiation site. The proximal 400 bp of the 5'-flanking region s hows a high G + C content (67%) and is part of a putative 1-kb CpG island t hat extends into exon I and part of intron 1. The putative promoter lacks a TATA box but contains two AP-1 sites and a conservatively defined consensu s GC box, the latter characteristic of the core binding sequence of the Spl transcription factor. (C) 2001 Academic Press.