Department of Microbiology, University of Washington, Seattle 98195-7242, USA.
The argH gene encoding argininosuccinate lyase (ASL) of Methanococcus maripaludis was cloned on a 4.7-kb HindIII genomic fragment. The gene is preceded by a short open reading frame (ORF149), which encodes a polypeptide with an unknown function. The two genes are co-transcribed. The ASL of M. maripaludis shares a high amino acid identity with ASLs from both bacterial and eukaryal origins and was able to complement both an argH Escherichia coli mutant and an arg4 yeast mutant, showing its extraordinary evolutionary conservation. Attempts to create an argH auxotroph of M. maripaludis by disrupting the genomic allele were unsuccessful: although a knockout allele of argH was integrated into the M. maripaludis chromosome by homologous recombination, the intact copy was not excluded, suggesting that the argH gene is essential.