Autophosphorylation at
tyrosine is a common process in eukaryotic
kinases, which is generally modulated by regulatory ligands and affects the properties of these
enzymes. We report that this type of modification occurs also in
bacteria, namely in an 81 kDa protein from
Acinetobacter johnsonii. This protein is
phosphorylated at the expense of ATP exclusively at
tyrosine residues. It is located in the inner-membrane fraction of cells and can be totally solubilized by detergents. It has been purified to homogeneity by antiphosphotyrosine immunochromatography. Analysis of the
peptides released under
trypsin proteolysis of the protein has shown that it autophosphorylates at several
tyrosine residues. The discovery of protein autophosphorylation in
bacteria seems of special interest for studying the regulatory aspects of this modification when considering the relative simplicity of the
bacterial systems, as compared with most eukaryotic systems, namely in terms of physiology and
genetics.
