Yield of FK506 by different strains of S. tsukubaensis . Bars encompass 95% of the sample population. Horizontal line representing the median values, and perpendicular lines indicating extreme values (min, max). Asterisks where representing statistically significant differences between different samples compared to control wild type samples (WT). The data were analyzed using SAS/STAT program as described in Methods. Introduction of additional “in trans” copies of target putative regulatory genes using phiC31-based integrative vector [WT-wild type, WT:R-fkbR over-expressed, WT:N-1 (shorter version of fkbN over-expressed), WT:N-fkbN over-expressed, inactivation of target putative regulatory S. tsukubaensis genes (ΔR-fkbR inactivated, ΔN-fkbN inactivated) and complementation experiments (ΔR:R-fkbR mutant complemented with fkbR, ΔRN:N-fkbR, fkbN double mutant complemented only with fkbN, ΔN:N-fkbN mutant complemented with fkbN)].