Fig. 4. The presence or absence of L chains dictates the site of RB accumulation. HeLa Tet-Off cells were transiently transfected with µCH1 expression vectors alone (a,d,g) or in combination with wild-type (L; b,e,h) or with a mutant lacking the constant domain (V_L; c,f). µCH1 appears red, whereas Ac38 and ERGIC-53 are green; bar 5 µm. g and h are imagines of resin-embedded EM sections. In cells expressing L chains, numerous ribosomes are uniformly distributed on the RB membrane. Electron density of RB content demonstrates high protein density. Bars, 200 nm.