Table II. On-target versus off-target binding.

	Total binders	On target	Fraction
AB1	42,386	466	1.10 × 10−2
HA	1608	53	3.30 × 10−2
4C1	2561	276	1.08 × 10−1
FLAG	7563	0	0
DM1A	44,821	207	4.62 × 10−3
A10	44,924	37	8.24 × 10−4
AB8	46,327	1	2.16 × 10−5
2C11	671	0	0

This table shows the number of peptides for each antibody that yielded a signal greater than 5-fold above background (“total binders”) and how many of those had at least 80% sequence identity with the true epitope (“on target”). See Table I for a list of true epitopes. A very low percentage (<11%) of the binding peptides had strong sequence similarity with the true epitope, in agreement with previous studies (24).