Phosphate-containing proteins of Salmonella typhimurium and Escherichia coli. Analysis by a new two-dimensional gel system.

The pattern of post-translational protein modifications involving a phosphate group was determined in the prokaryotes Salmonella typhimurium and Escherichia coli. A special two-dimensional gel electrophoretic separation was developed which utilizes acidic urea in the first dimension and neutral sodium dodecyl sulfate in the second dimension. This system allows survival and visualization of a number of proteins which are otherwise lost in systems employing basic conditions. The total number of phosphate-containing proteins thus obtained is approximately twenty. Among them are included proteins containing nucleotidylyl groups; two of these have been identified: glutamine synthetase (adenylylated) and regulatory protein PII (uridylylated). Two phosphate-containing proteins are shown to be regulated by the level of K+. The pattern of phosphorylation is shown to change with changing growth conditions and with specific mutations.