Modular arrangement of functional domains along the sequence of an aminoacyl tRNA synthetase.

Gene deletions show that much of Escherichia coli alanine tRNA synthetase is dispensable for each of three activities and that these activities appear to require specific domains arranged linearly along the polypeptide. Thus, variable fusions of extra polypeptide domains to a catalytic core may account for the diverse of aminoacyl tRNA synthetases.