def reverse_transcript_rna_char(base_char: str) -> str:
    """
    A function that reverse transcripts mRNA char into DNA char
    returns '' when base char is not one of RNA bases
    :param base_char:
    :return rna_char:
    """
    dict_of_rna_to_dna_base = {'A': 'T',
                               'U': 'A',
                               'C': 'G',
                               'G': 'C'}
    try:
        rna_char = dict_of_rna_to_dna_base[base_char]

    except KeyError:
        rna_char = ''

    return rna_char