The Ski-interacting protein SKIP/SNW1 associates with the P-TEFb/CDK9 elongation 
factor and coactivates inducible genes, including HIV-1. We show here that SKIP 
also associates with c-Myc and Menin, a subunit of the MLL1 histone 
methyltransferase (H3K4me3) complex and that HIV-1 Tat transactivation requires 
c-Myc and Menin, but not MLL1 or H3K4me3. RNAi-ChIP experiments reveal that SKIP 
acts downstream of Tat:P-TEFb to recruit c-Myc and its partner TRRAP, a scaffold 
for histone acetyltransferases, to the HIV-1 promoter. By contrast, SKIP is 
recruited by the RNF20 H2B ubiquitin ligase to the basal HIV-1 promoter in a 
step that is bypassed by Tat and downregulated by c-Myc. Of interest, we find 
that SKIP and P-TEFb are dispensable for UV stress-induced HIV-1 transcription, 
which is strongly upregulated by treating cells with the CDK9 inhibitor 
flavopiridol. Thus, SKIP acts with c-Myc and Menin to promote HIV-1 Tat:P-TEFb 
transcription at an elongation step that is bypassed under stress.