def add_target_columns(design_df, transcript_id_col='Target Transcript',
                       cut_pos_col='Target Cut Length',
                       transcript_base_col='Transcript Base'):
    """Add ['AA Index' and 'Transcript Base'] to design df

    :param design_df: DataFrame
    :return: DataFrame
    """
    out_df = design_df.copy()
    out_df['AA Index'] = (out_df[cut_pos_col] - 1) // 3 + 1
    out_df[transcript_base_col] = out_df[transcript_id_col].str.split('.', expand=True)[0]
    return out_df