Histone-binding component that specifically recognizes H3 tails trimethylated on 'Lys-4' (H3K4me3), which mark transcription start sites of virtually all active genes. The PHD-type zinc finger mediates the binding to H3K4me3. Belongs to the Alfin family. Lacks the Tyr (here Asp-212), a conserved feature of the aromatic cage required for the interaction with histone H3K4me3/2.