THE 57-KILODALTON PHOSPHOPROTEIN OF SPIROPLASMA-MELLIFERUM IS AUTOPHOSPHORYLATED

The partially purified 57-kDa protein of Spiroplasma melliferum was au tophosphorylated when incubated with ATP in the presence of ZnCl2. Aut ophosphorylation was also apparent by showing the in situ phosphorylat ion of the 57-kDa protein band separated by polyacrylamide gel electro phoresis under nondenaturing conditions, The autophosphorylation was a ffected neither by the pH of the reaction mixture nor by the presence of NaF. The steady state level of the phosphorylated 57-kDa protein re mained constant for up to 15 min, suggesting the absence of a phosphop rotein phosphatase activity in the preparation, As the initial phospho rylation rate did not decrease upon a 100-fold dilution of the 57-kDa protein under constant substrate concentration, it is suggested that t he autophosphorylation is an intramolecular process.