təɡˌɛðɚ wɪð ˈɑːɹ. dˈiː. kˈɑːɡhɪl, dʒˈɑːnsən wʌzðə fˈɜːst tə dɪskˈʌvɚ ðɪ ɛɡzˈɪstəns ʌv fˈaɪvmˈɛθəlsˌɪɾəsˌaɪn ɪn nˈeɪtʃɚ, fɹʌm tˌuːbɚkjʊlˈɪnɪk ˈæsɪd, ɐ nˈuːklɪˌɑːɾaɪd ʌv mˌaɪkəbɐktˈɪɹiəm tˌuːbɚkjʊlˈoʊsɪs.
Together with R. D. Coghill, Johnson was the first to discover the existence of 5-methylcytosine in nature, from tuberculinic acid, a nucleotide of Mycobacterium tuberculosis.