The invention relates to new proteins called alkylcytosine transferases (ACTs) derived from O
6
-alkylguanine-DNA alkyltransferase, and to substrates for ACTs specifically transferring a label to these ACTs and to fusion proteins comprising these. The substrates according of the invention are substituted cytosines of formula (I) wherein R
1
is an aromatic or a heteroaromatic group, or an optionally substituted unsaturated alkyl, cycloalkyl or heterocyclyl group with the double bond connected to OCH
2
—; R
2
is a linker; and L is a label or a plurality of same or different labels. The invention further relates to methods of transferring label L from these substrates of formula (I) to ACTs and ACT fusion proteins. The system of ACT-compound of formula (I) is particularly suitable for double labelling studies together with the known system O
6
-alkylguanine-DNA alkyltransferase (AGT)-benzylguanines.
本发明涉及一种称为烷基
胞嘧啶转移酶(ACT)的新蛋白质,该蛋白质来源于O6-烷基
鸟嘌呤-DNA烷基转移酶,以及用于将标签转移给这些ACT的底物和包含它们的融合蛋白质。本发明的底物是公式(I)中的取代
胞嘧啶,其中R1是芳香或杂芳基团,或者是具有双键连接到OCH2-的可选取代不饱和烷基、环烷基或杂环基团;R2是连接基;L是标签或相同或不同的多个标签。本发明还涉及将标签L从公式(I)的这些底物转移给ACT和ACT融合蛋白质的方法。ACT-化合物系统的公式(I)特别适用于与已知的O6-烷基
鸟嘌呤-DNA烷基转移酶(AGT)-苯甲基
鸟嘌呤一起进行双重标记研究。