Nature 401, 485— 489 (1999).

In this paper, part of the labelling of Fig. 3 was printed incorrectly. The half-tones of Fig. 3a should have been labelled from left to right: Anti-Tom22 (lanes 1 and 2); Anti-Tom40 (lanes 3 and 4); Anti-Tom20 (lanes 5 and 6); Anti-Tom70 (lanes 7 and 8). In addition, the axes of the ordinates of Fig. 3b should have been labelled from top to bottom: Co-precipitated Tom20; Co-precipitated Tom22; Co-precipitated Tom70.