Nucleotide sequence of the Erwinia chrysanthemi NCPPB 1066 L-asparaginase gene

The complete nucleotide sequence of the Erwinia chrysanthemi NCPPB 1066 gene coding for the chemotherapeutic enzyme L-asparaginase has been determined. The structural gene consists of an open reading frame commencing with an ATG start codon of 1044 bp followed by a TGA stop codon. Confirmation of the nucleotide sequence was obtained by comparing the predicted amino acid (aa) sequence with that derived by N-terminal aa sequencing of the purified protein. The gene has been shown to code for a 21-aa signal peptide at its N terminus which closely resembles the signal peptides of other secreted proteins. In common with highly expressed Escherichia coli genes, little use is made of modulator codons. The predicted aa sequence of the enzyme exhibits 46% identity with the determined primary sequence of the E. coli L-asparaginase, although the predicted secondary structure of both proteins indicates more extensive homology. Downstream of the TGA stop codon is a G + C-rich region of dyad symmetry (delta G = -25.4 kcal) characteristic of E. coli Rho-independent transcription terminators. Upstream of the structural gene there are no sequences which bear a strong resemblance to the consensus -35 and -10 regions of E. coli promoters. A sequence is present (CTGGCTCTCCTCTTGAT), however, which exhibits strong homology to the nif promoter consensus sequence (CTGGCACN5TTGCA). Upstream of this region is a sequence which strongly resembles the consensus sequence for promoter regions which are subject to catabolite repression.