This follows the conventions of the NBRF (PIR) programs.
line1: Title of matrix line2: 23 characters representing the one-letter codes and defining the order that the matrix is stored in lines3 to 25 are format(23I3).
MULTALIGN reads the one_lettercode line and uses this as an index into the matrix that follows.
Examples: md.mat,up.mat,gc.mat. Source: the above example files.