Embodiments concern compositions and methods involving recombinant antibodies to histone post-translational modifications. The invention provides compositions and methods for histone methyltransferase assays. In certain embodiments, the compositions and methods involve a recombinant antibody that binds histone H3 fragment harboring biomarkers such as H3K9me3 mark, H3K4me3 mark, H3K36me3 mark, H3K27me3, H3K9me3 and H3S10phos or a recombinant antibody that binds histone H4 fragment harboring H4K20me3 mark.