PPL and polymyositis: In contrast, the preincubation of SRP with human sera containing autoantibodies against SRP proteins from a number of polymyositis patients (19-1, 17-1, 4-2 and 25-1) completely abolished the translocation of the secretory protein precursor PPL into ER-derived microsomes (Figure 1, cf. lanes 15, 16, 21, 22, 27, 28, 33 and 34).