CLONING AND SEQUENCE-ANALYSIS OF CDNA FOR A HUMAN HOMOLOG OF EUBACTERIAL ATP-DEPENDENT LON PROTEASES

Overlapping cDNA clones containing mRNA for a putative Lon protease (L onHS) were isolated from cDNA libraries prepared from human brain poly (A)(+) RNA. The determined nucleotide sequence contains a 2814-bp open reading frame with two potential initiation codons (positions 62-64 a nd 338-340). The 5'-terminal 337-nucleotide fragment of LonHS mRNA is highly enriched with G and C nucleotides and could direct synthesis of the LonHS N-terminal domain. More likely this region promotes initiat ion of protein synthesis from the second AUG codon in a cap-independen t manner. The amino acid sequence initiated at the second AUG codon in cludes 845 residues, over 30% of which are identical to those of eubac terial Lon proteases. Residues of the 'A' and 'B' motifs of NTP-bindin g pattern and a plausible catalytic serine residue are conserved in Lo nHS. Northern blot analysis revealed LonHS mRNA in lung, duodenum, liv er and heart, but not in thymus cells.