def _nuc_pad_missing(nuc_alns, gen_lens):
    """
    >>> _nuc_pad_missing(['AAAAAAA'], gen_lens=[3, 5, 4])
    ['***', 'AAAAAAA', '****']
    """
    assert len(gen_lens) == len(nuc_alns) * 2 + 1
    alns = []
    for i, aln in enumerate(nuc_alns):
        alns.append('*' * gen_lens[i * 2])
        alns.append(aln)
    alns.append('*' * gen_lens[-1])
    return alns
