Abbott J, Marzluff W F, Gall J G
Department of Embryology, Carnegie Institution, Baltimore, Maryland 21210, USA.
Mol Biol Cell. 1999 Feb;10(2):487-99. doi: 10.1091/mbc.10.2.487.
The stem-loop binding protein (SLBP1) binds the 3' stem-loop of histone pre-mRNA and is required for efficient processing of histone transcripts in the nucleus. We examined the localization of SLBP1 in the germinal vesicle of Xenopus laevis oocytes. In spread preparations of germinal vesicle contents, an anti-SLBP1 antibody stained coiled bodies and specific chromosomal loci, including terminal granules, axial granules, and some loops. After injection of myc-tagged SLBP1 transcripts into the oocyte cytoplasm, newly translated myc-SLBP1 protein was detectable in coiled bodies within 4 h and in terminal and axial granules by 8 h. To identify the region(s) of SLBP1 necessary for subnuclear localization, we subcloned various parts of the SLBP1 cDNA and injected transcripts of these into the cytoplasm of oocytes. We determined that 113 amino acids at the carboxy terminus of SLBP1 are sufficient for coiled body localization and that disruption of a previously defined RNA-binding domain did not alter this localization. Coiled bodies also contain the U7 small nuclear ribonucleoprotein particle (snRNP), which participates in cleavage of the 3' end of histone pre-mRNA. The colocalization of SLBP1 and the U7 snRNP in the coiled body suggests coordinated control of their functions, perhaps through a larger histone-processing particle. Some coiled bodies are attached to the lampbrush chromosomes at the histone gene loci, consistent with the view that coiled bodies in the oocyte recruit histone-processing factors to the sites of histone pre-mRNA transcription. The non-histone chromosomal sites at which SLBP1 is found include the genes coding for 5 S rRNA, U1 snRNA, and U2 snRNA, suggesting a wider role for SLBP1 in the biosynthesis of small non-spliced RNAs.
茎环结合蛋白（SLBP1）与组蛋白前体mRNA的3'茎环结合，是细胞核中组蛋白转录本高效加工所必需的。我们研究了SLBP1在非洲爪蟾卵母细胞生发泡中的定位。在生发泡内容物的铺展制剂中，抗SLBP1抗体对卷曲小体和特定染色体位点进行了染色，包括末端颗粒、轴状颗粒和一些环。将带有myc标签的SLBP1转录本注射到卵母细胞细胞质中后，新翻译的myc-SLBP1蛋白在4小时内可在卷曲小体中检测到，8小时后可在末端和轴状颗粒中检测到。为了确定SLBP1亚核定位所需的区域，我们亚克隆了SLBP1 cDNA的各个部分，并将这些转录本注射到卵母细胞的细胞质中。我们确定SLBP1羧基末端的113个氨基酸足以实现卷曲小体定位，并且先前定义的RNA结合结构域的破坏不会改变这种定位。卷曲小体还含有U7小核核糖核蛋白颗粒（snRNP），它参与组蛋白前体mRNA 3'末端的切割。SLBP1和U7 snRNP在卷曲小体中的共定位表明它们的功能可能通过一个更大的组蛋白加工颗粒进行协调控制。一些卷曲小体在组蛋白基因位点处附着于灯刷染色体，这与卵母细胞中的卷曲小体将组蛋白加工因子募集到组蛋白前体mRNA转录位点的观点一致。发现SLBP1的非组蛋白染色体位点包括编码5 S rRNA、U1 snRNA和U2 snRNA的基因，这表明SLBP1在小非剪接RNA的生物合成中具有更广泛的作用。
