FIG. 2.
Native E7 production in wt L. lactis depends on growth phase. E7 production and secretion were analyzed by Western blotting from cultures induced at different times such that 1 h after induction, the samples were harvested at exponential (OD600 ≈ 0.5 to 0.6) or stationary (OD600 ≈ 1.5) phase. Strains contain plasmid pCYT-E7 (encoding native E7, cytoplasmic form) or pSEC-E7 (encoding the precursor preE7, i.e., SPUsp45 fused to E7). (A) Exponential-phase cultures. Noninduced (−) and induced (+) cultures of wt L. lactis containing plasmids are as indicated. (B) Stationary-phase cultures. Arrows indicate positions of E7 mature and precursor forms. There is only a slight difference in migration positions of the preE7 (in cell lysates) and the secreted E7 mature form (in supernatant fraction). Abbreviations: C, cell lysates; S, supernatant fraction; M, positions and sizes of molecular mass markers.