Propionyl-CoA carboxylase (PCC, EC 6.4.1.3) is a mitochondrial, biotin-dependent 
enzyme that functions in the catabolism of branched-chain amino acids, fatty 
acids with odd-numbered chain lengths, and other metabolites. It catalyzes the 
ATP-dependent carboxylation of propionyl-CoA to d-methylmalonyl-CoA. PCC is 
composed of two types of subunits, likely as alpha4beta4 or alpha6beta6, with 
the alpha subunit containing the covalently bound biotin prosthetic group. A 
genetic deficiency of PCC activity causes propionic 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 PCCA gene which, at the present time, 
is only partially represented in the databases. Based on reported ESTs and 
confirmed by RT-PCR, we also redefine the 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 mutations to count from the new initiation codon. The 
gene spans more than 360 kb 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 approximately 1 kb of the 5'-flanking 
region upstream of the ATG translation initiation site. The proximal 400 bp of 
the 5'-flanking region shows a high G + C content (67%) and is part of a 
putative 1-kb CpG island that extends into exon 1 and part of intron 1. The 
putative promoter lacks a TATA box but contains two AP-1 sites and a 
conservatively defined consensus GC box, the latter characteristic of the core 
binding sequence of the Sp1 transcription factor.