Replication-dependent histone mRNAs are the only cellular mRNAs that are not polyadenylated, ending in a stemloop instead of a polyA tail, and are normally regulated coordinately with DNA replication. Stemloop-binding protein (SLBP) binds the 3' end of histone mRNA, and is required for processing and translation. During Drosophila oogenesis, large amounts of histone mRNAs and proteins are deposited in the developing oocyte. The maternally deposited histone mRNA is synthesized in stage 10B oocytes after the nurse cells complete endoreduplication. We report that in wild-type stage 10B oocytes, the histone locus bodies (HLBs), formed on the histone genes, produce histone mRNAs in the absence of phosphorylation of Mxc, which is normally required for histone gene expression in S-phase cells. Two mutants of SLBP, one with reduced expression and another with a 10-amino-acid deletion, fail to deposit sufficient histone mRNA in the oocyte, and do not transcribe the histone genes in stage 10B. Mutations in a putative SLBP nuclear localization sequence overlapping the deletion phenocopy the deletion. We conclude that a high concentration of SLBP in the nucleus of stage 10B oocytes is essential for histone gene transcription.

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复制依赖性组蛋白 mRNA 是唯一未聚腺苷酸化的细胞 mRNA，以茎环而非聚腺苷酸尾结尾，并且通常与 DNA 复制协调调节。茎环结合蛋白 (SLBP) 结合组蛋白 mRNA 的 3' 末端，是加工和翻译所必需的。在果蝇卵子发生过程中，大量组蛋白 mRNA 和蛋白质沉积在发育中的卵母细胞中。母体沉积的组蛋白 mRNA 在护士细胞完成核内复制后在 10B 期卵母细胞中合成。我们报道，在野生型 10B 期卵母细胞中，组蛋白基因上形成的组蛋白基因座体 (HLB) 在​​没有 Mxc 磷酸化的情况下产生组蛋白 mRNA，而 Mxc 磷酸化通常是 S 期细胞中组蛋白基因表达所必需的。 SLBP 的两种突变体，一种表达减少，另一种缺失 10 个氨基酸，无法在卵母细胞中沉积足够的组蛋白 mRNA，并且在 10B 阶段不转录组蛋白基因。假定的 SLBP 核定位序列中的突变与缺失表型重叠。我们得出结论，10B 期卵母细胞核中高浓度的 SLBP 对于组蛋白基因转录至关重要。

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