Patent ID: 7547513

Claim:
Process for mutating a protein X selected from the kinases belonging to the EC 2.7.1-classes, the nucleotidyl transferases belonging to the EC 2.7.7-classes, and the phosphorylases belonging to the EC 2.4.2-classes, in order to obtain a mutated protein having an extended activity compared with the initial protein X, wherein the process comprises: a) providing cells comprising a genotype [protein Y*::protein X+], wherein i) Y* signifies that the gene coding for protein Y has been inactivated to create a deficiency of protein Y in said cells, ii) Y is a protein having a four-digit EC class designation related to a four-digit EC class designation of protein X in that at least the first three digits of the EC class designation of protein Y are the same as the corresponding first three digits of the EC class designation of protein X, iii) said cells comprise the gene coding for protein X, and iv) said cells have an auxotrophic phenotype requiring for survival the presence of the product of the reaction of protein Y on its substrate; b) exposing the cells obtained in a) to a promutagenic nucleoside analogue for mutation to form the mutated protein of protein X; c) culturing said cells in a medium comprising a substrate of Y in an amount sufficient for the survival of said cells; and d) selecting the cell or cells, which have survived c), and in which the mutated protein X complements the deficiency of protein Y in the cell or cells.