The SAR domain of Lyz is sufficient for localization in both membrane and soluble compartments. (A) The N-terminal domain of Lyz confers partial membrane localization on soluble proteins. Total membrane and soluble fractions were prepared from induced cultures of XL1-Blue cells carrying pJFLyz (lanes 1–2), TG1 cells carrying pJFLyzΦPhoA (lanes 3–4), pJFPhoA (lanes 5–6), or pcmycLyzΦ19 (lanes 7–8), and were analyzed by SDS/PAGE and immunoblotting as described in Materials and Methods. s, soluble fractions; m, membrane fractions. (B) The N terminus of the phage 21 endolysin is a functional SAR sequence. Total membrane and soluble fractions were prepared from induced cultures of XL1-Blue cells carrying pJFFtsIΦLyz (lanes 2–3), pJFR21cmyc (lanes 4–5), or pJFR21ΦLyz (lanes 6–7), and were analyzed by SDS/PAGE and immunoblotting as described in Materials and Methods. The masses of the prestained standards (lane 1) are given in kDa on the left.