Effects of leader sequences on the growth of E. coli BL21 cells expressing chlamydial porins. A. Moderate inhibition of bacterial (BL21) growth during expression of C. trachomatis MOMP containing native (nL-TR) and OmpT (oT-TR) leaders, contrasting with lack of significant inhibition during expression of mature, leaderless C. trachomatis MOMP (TR). B. Slight inhibition of bacterial growth during expression of C. muridarum MOMP with its native leader (nL-MU, compare to BL21 in A), contrasting with strong inhibition when Ch. abortus MOMP is expressed with its native leader (nL-AB). Cell growth is markedly reduced with both native-leadered PorB (nL-PB) and OmpT-leadered PorB (oT-PB). Note the "recovery" as non-resistant organisms overgrow in β-lactamase-containing cultures (see text). Measurements are means ± SEM (n = 4 independent experiments).