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Expression of genes involved in nikkomycin production in Streptomyces tendae was investigated by two-dimensional gel electrophoresis of cellular proteins. Ten gene products (P1-P10) were identified that were synthesized when nikkomycin was produced; these proteins were not detected in non-producing mutants. N-terminal sequences of six of the 10 proteins were obtained by microsequencing of protein spots excised from preparative two-dimensional gels. Protein P8 was identified as L-histidine amino-transferase (HisAT), which has been previously correlated with nikkomycin production. By using oligonucleotide probes deduced from the N-terminal sequences of protein P2 and P6, we isolated an 8 kb BamHI fragment and a 6.5 kb PvuII fragment, respectively, from the genome of Streptomyces tendae Tü901. Restriction analyses revealed that both fragments overlapped within a region of 1.5 kb. Mapping of the oligonucleotide probe hybridizing sites indicated that the genes encoding protein P2 and P6 are closely spaced on the 8 kb BamHI fragment, and the latter is located on the overlapping region. DNA sequence analysis revealed that proteins P1 and P2 are encoded by a single gene, orfP1, that is translated at two initiation codons. The orfP1 gene was interrupted by homologous recombination using the integrating vector pWHM3. The gene-disrupted transformants did not produce nikkomycin, indicating that proteins P1 and P2 are essential for nikkomycin production. The data presented show that reverse genetics was successfully used to isolate genes involved in nikkomycin production.
Möhrle et al. (Wed,) studied this question.