Signal sequences are not uniformly hydrophobic

A sample of 34 hydrophobia core-segments from known signal sequences have been analysed with regard to the mean hydrophobicity at each position in the segment. The results show that these core-segments are not uniformly hydrophobic; instead, the more hydrophobic residues are concentrated around the midpoints of the segments. A similar analysis carried out on a sample of 12 membrane-spanning segments from transmembrane proteins indicates that the hydrophobic residues are much more evenly distributed along the segments in this case.