Table 1.

Calculated and observed masses for the subcomplexes generated by increasing the ionic strength from 250 mM to 500 mM AmAc

No.	Subcomplexes	Calculated mass, Da	Observed mass, Da
0	(k, l, e, d, c, a, b, i, g, j, f, h, m)	794,310	797,999 ± 180
1	(k, l, e, d, c, b, i, g, f, h, m)	598,898	600,501 ± 93
2	(e, d, c, b, i, g, f, h, m)	507,286	508,830 ± 23
3	(k, l, e, d, c, h, f, m)	434,379	434,885 ± 157
4	(k, l, e, d, c, h, f)	391,695	392,199 ± 36
5	(k, l, e, d, c, h)	354,489	354,978 ± 27
6	(k, l, e, d, c)	314,578	314,868 ± 93
7	(a, b, i, g, c)	437,811	438,478 ± 26
8	(a, b, i, g, e)	383,090	383,524 ± 26
9	(k, l, e, d, c, i, g)	386,631	386,950 ± 77
10	(l, e, d, c, h, f, m)	409,347	410,081 ± 72
11	(l, e, d, c, h, f)	366,993	367,285 ± 108
12	(l, e, d, c, h)	329,517	329,820 ± 90
13	(l, e, d, c)	289,606	290,003 ± 63
14	(k, l, e, c)	250,600	250,965 ± 55
15	(k, l, e, d)	207,791	207,872 ± 17
16	(l, e, d)	182,820	182,861 ± 49
17	(e, d)	116,180	116,199 ± 36
18	(b, i, g)	164,518	164,680 ± 9
19	(i, g)	71,985	72,108 ± 2
20	(b, g)	128,015	128,102 ± 21
21	(f, h, m)	119,740	119,742 ± 5
22	(f, h)	77,321	77,322 ± 5
23	(h, m)	82,264	82,268 ± 2
24	(f, m)	79,890	79,931 ± 23
25	(k, l, e)	143,749	143,819 ± 49
26	(k, l)	91,616	91,636 ± 7
27	(l, e)	118,777	118,786 ± 37

Calculated masses are the sum of the measured masses determined for the individual subunits by using HPLC/MS with the exception of eIF3a, which could not be measured with sufficient accuracy. The sequence mass of eIF3a was used in this case. Assignment based on mass alone was rarely possible. Tandem MS and observation of series of subcomplexes were used to limit our search and enable a unique assignment.