The adpA and 5913 genes contain TTA DNA sequences that specify UUA codons, which require the tRNA product of the bldA gene in order to be translated. 5913 is an extracellular protease that negatively regulates the protease inhibitor STI (Streptomyces trypsin inhibitor), which binds to and inhibits 1355, an extracellular protease proposed to cleave proproteins required for aerial hyphae formation. An unidentified peptide signal imported by BldK may induce expression of 5913, although this is speculative, as indicated by the question mark.