Methods for increasing molecular diversity of polyketides and non-ribosomal proteins

A process for producing a library of two or more mutant modular polyketide synthase encoding cells which express mutant functional polyketide synthases having an increased or reduced number of modules and which have been formed by recombination events which process comprises the steps of:

• (i) contacting a modular polyketide synthase encoding strain of cells with a vector which includes a selectable marker and a portion of DNA homologous to a portion of DNA within the polyketide synthase such that the vector integrates into cells of the strain via a single crossover event;
• (ii) applying selective pressure to the cells into which the vector has been integrated so that the cells eliminate the selectable marker through one or more recombination events;
• and
• (iii) screening for or selecting two or more cells that lack the selectable marker and which express mutant functional polyketide synthases having an increased or reduced number of modules.