In 1993, a new base, beta-d-glucopyranosyloxymethyluracil (base J), was identified in the nuclear DNA of Trypanosoma brucei. Base J is the first hypermodified base found in eukaryotic DNA. It is present in all kinetoplastid flagellates analyzed and some unicellular flagellates closely related to trypanosomatids, but it has not been found in other protozoa or in metazoa. J is invariably present in the telomeric repeats of all organisms analyzed. Whereas in Leishmania nearly all J is telomeric, there are other repetitive DNA sequences containing J in T. brucei and T. cruzi, and most J is outside telomeres in Euglena. The biosynthesis of J occurs in two steps: First, a specific thymidine in DNA is converted into hydroxymethyldeoxyuridine (HOMedU), and then this HOMedU is glycosylated to form J. This review discusses the identification and localization of base J in the genome of kinetoplastids, the enzymes involved in J biosynthesis, possible biological functions of J, and J as a potential target for chemotherapy of diseases caused by kinetoplastids.

中文翻译：

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基础 J：发现、生物合成和可能的功能。

1993 年，在布氏锥虫的核 DNA 中发现了一个新的碱基，β-d-吡喃葡萄糖基氧甲基尿嘧啶（碱基 J）。碱基 J 是在真核 DNA 中发现的第一个超修饰碱基。它存在于所有分析的动质体鞭毛虫和一些与锥虫密切相关的单细胞鞭毛虫中，但在其他原生动物或后生动物中未发现。J 总是存在于所有被分析生物的端粒重复序列中。而在利什曼原虫中，几乎所有 J 都是端粒，而在 T. brucei 和 T. cruzi 中还有其他包含 J 的重复 DNA 序列，并且大多数 J 在 Euglena 的端粒之外。J 的生物合成分两步进行：首先，DNA 中的特定胸苷转化为羟甲基脱氧尿苷 (HOMedU)，然后该 HOMedU 被糖基化形成 J。