Molecular structure of ilvIH and its evolutionary relationship to ilvG in Escherichia coli K12

Abstract

ilvIH of Escherichia coll K12 codes for a vallne-sensltlve acetohydroxy acid synthase (AHASIII). The DNA sequence of ilvIH was determined. Open reading frames and appropriate translation signals exist for two polypeptides, one containing 565 amino acids (ilvl polypeptide) and the other 160 amino acids (ilvH polypeptide). A graphic matrix analysis shows three clearcut regions of homology between ilvl and llvG (codes for AHASII). Within these three regions of homology, 50-60% of the amino acid sequences of AHASII and AHASIII are conserved. Inspection of the region between ilvG and ilvE (the K region) revealed that it can potentially code for an 86 amino acid polypeptide. A computer analysis shows small but significant homology between the predicted amino acid sequences of the N-terminal half of the ilvH polypeptide and the putative region K polypeptide. We conclude that ilvIH and ilvG-region K evolved from a common ancestor. © 1983 IRL Press Limited.