FIG. 2.

Decreased levels of PrsA protein affect only a late stage of secretion. Saturation of the secretion apparatus by overexpressed AmyQ in cells with a low level of PrsA was determined. IH7673 (P_spac-prsA P_xyn-amyQ) was grown in modified 2× L broth supplemented either with 24 μM or 1 mM IPTG. At a cell density of Klett 100, expression of P_xyn-amyQ was induced as described in the legend to Fig. 1. Cell and medium fractions were prepared, and PrsA and AmyQ content in the fractions was analyzed by ECL. The analyzed samples were from 40 μl (PrsA; top) or 7.5 μl (secreted AmyQ; middle) of culture, or as indicated (cell-associated AmyQ; bottom). Precursor (p) and mature (m) forms and degradation product (d) are indicated by arrows.