replication-dependent histone mRNAs
Metazoan replication-dependent histone mRNAs are the only eukaryotic mRNAs that lack polyA tails. The genes for the five histone proteins have remained physically linked during evolution.
Expression of histone mRNAs and histone proteins requires a unique set of factors, and may be coordinated by association of the histone genes with Cajal bodies.
Several novel factors, including components of the U7 snRNP, as well as proteins involved in regulation of histone gene expression, have been described.
References
Marzluff WF. Metazoan replication-dependent histone mRNAs: a distinct set of RNA polymerase II transcripts. Curr Opin Cell Biol. 2005 Jun;17(3):274-80. PMID: #15901497#