Table 1. M26 and I26 have highest conservation in gp160 sequences An alignment of 4236 gp160 sequences (Supplementary file 1) was used to compare absolute occurrence of each amino acid in position 26 of the signal peptide (SP) and the respective cleavable SP probability predicted by SignalP 3.0.

Position 26	SP probability	Absolute occurrence
Y	0.458	0
I	0.51	1375
F	0.591	7
V	0.604	16
M	0.628	2638
L	0.697	143
C	0.699	1
W	0.751	1
T	0.777	39
G	0.792	0
A	0.805	2
S	0.848	5
K	0.863	0
Q	0.897	0
E	0.901	4
D	0.906	0
R	0.909	3
N	0.923	0
H	0.928	1
P	0.928	1