The HIV-1 transactivator protein Tat is a critical regulator of HIV transcription primarily enabling efficient elongation of viral transcripts. Its interactions with RNA and various host factors are regulated by ordered, transient posttranslational modifications (PTMs). Here, we report a novel Tat modification, monomethylation at lysine-71 (K71). We found that K71 monomethylation (K71me) is catalyzed by KMT7, a methyltransferase that also targets lysine-51 (K51) in Tat. Using mass spectrometry, in vitro enzymology, and modification-specific antibodies, we found that KMT7 monomethylates both K71 and K51 in Tat. K71me is important for full Tat transactivation, as KMT7 knockdown impaired the transcriptional activity of wild type (WT) Tat but not a Tat K71R mutant. These findings underscore the role of KMT7 as an important monomethyltransferase regulating HIV transcription through Tat.
The HIV-1 Tat protein is monomethylated at lysine-71 by the lysine methyltransferase KMT7.