def writeClustal(filename, msa):
    """A simple writer for CLUSTAL format alignments.

    This lacks the characters showing degree of conservation
    but otherwise conforms to the CLUSTAL format standards."""
    msafile = open(filename, 'w')
    msafile.write('CLUSTALW file written by ProDy\n\n')
    for j in range(msa.numResidues() / 60):
        for i in range(msa.numSequences()):
            sequence = str(msa[i])
            msafile.write(msa.getLabel(i) + ' ' * (16 - len(msa.getLabel(i))))
            msafile.write(sequence[j * 60:(j + 1) * 60])
            msafile.write('\n')
        msafile.write('\n\n')
    for i in range(msa.numSequences()):
        sequence = str(msa[i])
        msafile.write(msa.getLabel(i) + ' ' * (16 - len(msa.getLabel(i))))
        msafile.write(sequence[(j + 1) * 60:])
        msafile.write('\n')
    msafile.close()
    return
