SRP54 and polymyositis: We found that the IgG fractions from polymyositis patients containing anti-SRP54 autoantibodies (sera 17-1, 19-1, 25-1, 4-2), but not from polymyositis patients without myositis autoantibodies or with other specificities (sera 1–24, 5–15), significantly reduced the crosslinking of SRP54 to the PPL signal sequence (Figure 4a, lanes 3–8, PPL86/SRP54, white arrowheads).