In metazoans, histone mRNAs are not polyadenylated but end in a conserved stem-loop. Stem-loop binding protein (SLBP) binds to the stem-loop and is required for all steps in histone mRNA metabolism. The genes for the five histone proteins are linked. A histone locus body (HLB) forms at each histone gene locus. It contains factors essential for transcription and processing of histone mRNAs, and couples transcription and processing. The active form of U7 snRNP contains the HLB component FLASH (FLICE-associated huge protein), the histone cleavage complex (HCC), and a subset of polyadenylation factors including the endonuclease CPSF73. Histone mRNAs are rapidly degraded when DNA replication is inhibited by a 3′ to 5′ pathway that requires extensive uridylation of mRNA decay intermediates.

在后生动物中，组蛋白mRNA没有被聚腺苷酸化，而是以保守的茎环为末端。茎环结合蛋白（SLBP）与茎环结合，是组蛋白mRNA代谢中所有步骤所必需的。五个组蛋白的基因相互关联。组蛋白基因座体（HLB）在每个组蛋白基因基因座处形成。它包含对于组蛋白mRNA的转录和加工必不可少的因子，并将转录和加工耦合在一起。U7 snRNP的活性形式包含HLB组分FLASH（与FLICE相关的巨大蛋白质），组蛋白裂解复合物（HCC）和包括腺内切酶CPSF73在内的多聚腺苷酸化因子的子集。当DNA复制受到3'至5'途径的抑制时，组蛋白的mRNA会迅速降解，而这需要大量尿苷化mRNA降解中间体。