def reverse_transcribe(seq):
    """reverse transcribes a dna sequence (does not convert any non-atcg/ATCG characters)"""
    watson_crick = {'A': 'T', 'T': 'A', 'G': 'C', 'C': 'G', 'a': 't', 't': 'a', 'g': 'c', 'c': 'g'}
    return ''.join([watson_crick.setdefault(c, c) for c in seq[::-1]])