Fusion to Nuc rescue E7 in intracellular production and increase protein yields for the secreted forms of E7 and L7/L12. A. A DNA fragment encoding the mature moiety of Nuc was fused to the fragment encoding E7 (pCYT:Nuc:E7). Production of Nuc-E7 analyzed by Western blot using anti-E7 antibodies on protein samples prepared from induced cultures harvested either at exponential (exp) or stationary (stat) phase. Positions and sizes of molecular weight marker (M) are indicated at left. B. The mature Nuc fragment was inserted between SPUsp45 and the fragment encoding E7 (pSEC:Nuc:E7) or L7/L12 (pSEC:Nuc:L7/L12). Secretion of the fusion proteins was analyzed by Western blot using either anti-E7 or anti-L7/L12 antibodies. C, cell lysates; S, supernatant fraction. Positions of precursor (prec) or mature forms of E7, Nuc-E7, L7/L12, NucB-L7/L12, and NucA-L7/L12 are indicated by arrows.