def max_sequential_nt(mer1, mer2):
    """Returns the maximum number of nt that would bind between two kmers.

    :param kmer1: the first kmer
    :param kmer2: the second kmer (order unimportant)
    """
    binding = {'A': 'T', 'T': 'A', 'C': 'G', 'G': 'C', '_': False}
    if len(mer2) > len(mer1):
        mer1, mer2 = mer2, mer1
    mer1_len = len(mer1)
    mer2 = mer2[::-1]
    mer1 = mer1.ljust(mer1_len + len(mer2), '_')
    max_bind = 0
    for offset in range(mer1_len):
        consecutive = 0
        for x in range(len(mer2)):
            if binding[mer1[offset + x]] == mer2[x]:
                consecutive += 1
                if consecutive > max_bind:
                    max_bind = consecutive
            else:
                consecutive = 0
    return max_bind
