No abstract

Chick embryo liver mitochondrial matrix protein, 5‐aminolaevulinate synthase, is synthesised initially as a larger cytosolic precursor. In this report we present the complete nucleotide sequence of a cDNA clone coding for the precursor together with corresponding confirmatory amino acid sequence of peptides derived from purified mature mitochondrial enzyme. The deduced amino acid sequence shows that the precursor consists of mature enzyme of 579 amino acids and an N‐terminal extension of 56 amino acids. The latter presequence is highly basic in character as found with other mitochondrial preproteins.

5-Aminolevulinate synthase, the first and rate-controlling enzyme of heme biosynthesis, is regulated in the liver by the end-product heme. To study this negative control mechanism, we have isolated the chicken gene for ALA-synthase and determined the nucleotide sequence. The structural gene is 6.9 kb long and contains 10 exons. The transcriptional start site for ALA-synthase was determined by primer extension analysis. A fragment of 291 bp from the 5' flanking region including 34 bp of the first exon shows promoter activity when introduced upstream of a chicken histone H2B gene and injected into the nuclei of Xenopus laevis oocytes.