InterPro domain: IPR026502

This family consists of the histone stem-loop-binding protein (SLBP1) and the Xenopus Oocyte-specific histone RNA stem-loop-binding protein 2 (SLBP2). They both bind to the 3' end of histone mRNA in frog oocytes. However, their functions are different. SLBP1 participates in histone pre-mRNA processing in the nucleus, while oocyte specific SLBP2 doesn't support the histone pre-mRNA processing and locates in the cytoplasm [ 1 ].

SLBP1 binds the 5' side of the stem-loop structure of replication-dependent histone pre-mRNAs and contributes to efficient 3'-end processing by stabilising the complex between histone pre-mRNA and U7 small nuclear ribonucleoprotein (snRNP), via the histone downstream element (HDE) [ 2 ]. It plays an important role in targeting mature histone mRNA from the nucleus to the cytoplasm and to the translation machinery. It stabilises mature histone mRNA and could be involved in cell-cycle regulation of histone gene expression [ 3 , 4 , 5 , 6 ].

SLBP2 binds to translationally inactive histone mRNA stored in immature oocytes. When oocytes mature, SLBP2 is degraded and a larger fraction of the histone mRNA is bound to SLBP1. Instead of having a role in histone pre-mRNA processing, SLBP2 may be a specific translational repressor [ 7 ].

1. Two Xenopus proteins that bind the 3' end of histone mRNA: implications for translational control of histone synthesis during oogenesis. Mol. Cell. Biol. 19, 835-45
2. Drosophila stem loop binding protein coordinates accumulation of mature histone mRNA with cell cycle progression. Genes Dev. 15, 173-87
3. Stem-loop binding protein expressed in growing oocytes is required for accumulation of mRNAs encoding histones H3 and H4 and for early embryonic development in the mouse. Dev. Biol. 313, 347-58
4. Three proteins of the U7-specific Sm ring function as the molecular ruler to determine the site of 3'-end processing in mammalian histone pre-mRNA. Mol. Cell. Biol. 29, 4045-56
5. Phosphorylation of stem-loop binding protein (SLBP) on two threonines triggers degradation of SLBP, the sole cell cycle-regulated factor required for regulation of histone mRNA processing, at the end of S phase. Mol. Cell. Biol. 23, 1590-601
6. Knockdown of SLBP results in nuclear retention of histone mRNA. RNA 15, 459-72