Integration of MtLA into U-INV is dependent on 4.5S RNA. (A) Northern blot analysis using a 4.5S RNA probe (see MATERIALS AND METHODS for details). Lane 1, 25 μl of CTF (cytosolic translation factors); lane 2, flow-through (FT) of CTF applied to DEAE-Sepharose CL-6B; lane 3, 50 mM KOAc-eluate; lanes 4 and 5, 0.6 M KOAc-eluate before and after concentration by ultrafiltration, respectively; the latter was used as RNA-free CTF; lanes 6 and 7, 1 M and 2 M KOAc–eluates, respectively. (B) The RNA-free CTF after DEAE-treatment (lane 5) was used for in vitro synthesis of MtlA in the presence of 4.5S RNA-free tRNA (80 ng/μl final concentration) and the reagents indicated (INV, E. coli membrane vesicles; U-INV, urea-extracted INV; FtsY [20 ng/μl] and Ffh [8 ng/μl] indicate the purified proteins and the final concentrations used. 4.5S RNA, purified 4.5S RNA [1 ng/μl final concentration]; PK, Proteinase K [0.5 mg/ml final concentration]).