The stem-loop binding protein (SLBP1) is present in coiled bodies of the Xenopus germinal vesicle

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 th e nucleus. We examined the localization of SLBP1 in the germinal vesicle of Xenopus laevis oocytes. In spread preparations of germinal vesicle content s, an anti-SLBP1 antibody stained coiled bodies and specific chromosomal lo ci, including terminal granules, axial granules, and some loops. After inje ction of myc-tagged SLBP1 transcripts into the oocyte cytoplasm, newly tran slated 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 nece ssary for subnuclear localization, we subcloned various parts of the SLBP1 cDNA and injected transcripts of these into the cytoplasm of oocytes. We de termined that 113 amino acids at the carboxy terminus of SLBP1 are sufficie nt for coiled body localization and that disruption of a previously defined RNA-binding domain did not alter this localization. Coiled bodies also con tain the U7 small nuclear ribonucleoprotein particle (snRNP), which partici pates 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 t heir 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 hi stone-processing factors to the sites of histone pre-mRNA transcription. Th e non-histone chromosomal sites at which SLBP1 is found include the genes c oding for 5 S rRNA, U1 snRNA, and U2 snRNA, suggesting a wider role for SLB P1 in the biosynthesis of small non-spliced RNAs.