title: Single base substitutions at the initiator codon in the mitochondrial acetoacetyl-CoA thiolase (ACAT1/T2) gene result in production of varying amounts of wild-type T2 polypeptide.
abstract: Initiator codon mutations are relatively uncommon and less well characterized compared to other types of mutations. We identified a novel initiator codon mutation (c.2T>C) heterozygously in a Japanese patient (Patient GK30) with mitochondrial acetoacetyl-CoA thiolase (T2) gene deficiency (ACAT1 deficiency); c.149delC was on the other allele. We examined translation efficiencies of nine mutant T2 cDNAs harboring one-base substitutions at the initiator methionine codon using in vivo transient expression analysis. We found that all the mutants produced wild-type T2 polypeptide, to various degrees (wild type (100%) > c.1A>C (66%) > c.2T>C, c.3G>C, c.3G>T (22%) > c3G>A, c.1A>G (11%) > c.2T>A, c.2T>G, c.1A>T (7.4%)). T2 mRNA expression levels in Patient GK08 (a homozygote of c.2T>A) and Patient GK30 fibroblasts, respectively, were almost the same as in control fibroblasts, when examined using semiquantitative PCR. This means that initiator codon mutations did not affect T2 mRNA levels. We propose that all one-base substitutions at the initiator methionine codon in the T2 gene could be mutations, which retain some residual T2 activity.
authors.affiliation: Department of Pediatrics, Gifu University School of Medicine, Gifu, Japan. toshi-gif@umim.ac.jp
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Fukao
authors.forename: Naoki
authors.initials: N
authors.lastname: Matsuo
authors.forename: Gai Xiu
authors.initials: GX
authors.lastname: Zhang
authors.forename: Rintaro
authors.initials: R
authors.lastname: Urasawa
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Kubo
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kohno
authors.forename: Naomi
authors.initials: N
authors.lastname: Kondo
mesh_terms: D000101:Acetyl-CoA C-Acetyltransferase / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics*; D002460:Cell Line; D018387:Codon, Initiator / Q000235:genetics*; D004252:DNA Mutational Analysis; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D006579:Heterozygote; D006801:Humans; D007223:Infant; D007564:Japan; D008297:Male; D008928:Mitochondria / Q000201:enzymology* / Q000235:genetics*; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics*; D017354:Point Mutation / Q000235:genetics*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D018387:Codon, Initiator; D018076:DNA, Complementary; D010455:Peptides; D012333:RNA, Messenger; D000101:Acetyl-CoA C-Acetyltransferase