Primary and quaternary structure of the catabolic ornithine carbamoyltransferase from Pseudomonas aeruginosa

Extensive sequence homology with the anabolic ornithine carbamoyltransferases of Escherichia coli

Authors


Correspondence to D. Haas, Mikrobiologisches institut ETH, ETH-Zentrum, CH-8092 Zürich, Switzerland

Abstract

We have determined the complete nucleotide sequence of the arcB gene from Pseudomonas aeruginosa strain PAO and we have purified the arcB Product, the catabolic ornithine carbamoyltransferase (EC 2.1.3.3), to apparent homogeneity from the same strain. The N-terminal amino acid sequence, the total amino acid composition and the subunit size of the purified enzyme were in agreement with nucieotide sequencing results, which predict a polypeptide of 336 amino acids (Mr 38108). Crosslinking experiments suggest that the native enzyme (apparent Mr approx. 420000) basically consists of a trimer aggregating to form nonamers or dodecamers.

The arcB gene of P. aeruginosa had strong homology with the argF and argI genes which code for the anabolic ornithine carbamoyltransferase isoenzymes in Escherichia coli; 63% of the nucleotides and 57% of the amino acids were absolutely conserved in arcB and argF. This indicates a close evolutionary relationship between these genes although their products have different physiological functions in the cell.

Under conditions of induction (ennergy depletion) the catabolic ornithine carbamoyltransferase represented geqslant R: gt-or-equal, slanted 10% of the total cellular protein. Like other highly expressed Pseudomonas genes, the arcB gene was found not to use seven codons which correspond to minor or weakly interacting tRNA species in E. coli.

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