Abstract: The invention relates to methods and compositions for identifying a candidate nucleic acid (CNA) comprising a polynucleotide sequence encoding at least a part of a natural product gene cluster (NPGC), a secondary metabolite biosynthesis cluster (SMBC), a non ribosomal peptide (NRP), a polyketide (PK) biosynthesis cluster, a protein involved in NRP and/or PK biosynthesis, a protein involved in other secondary metabolite biosynthesis, and/or a phosphopantetheinyl transferase (PPTase), by expressing the candidate nucleic acid (CNA) to form at least one PPTase, incubating the PPTase with a non ribosomal peptide synthetase (NRPS), and detecting activation of the NRPS, wherein activation indicates that said CNA comprises a polynucleotide sequence encoding at least one of the above.