The polypeptide composition of the U7 small nuclear ribonucleoprotein (snRNP) 
involved in histone messenger RNA (mRNA) 3' end formation has recently been 
elucidated. In contrast to spliceosomal snRNPs, which contain a ring-shaped 
assembly of seven so-called Sm proteins, in the U7 snRNP the Sm proteins D1 and 
D2 are replaced by U7-specific Sm-like proteins, Lsm10 and Lsm11. This 
polypeptide composition and the unusual structure of Lsm11, which plays a role 
in histone RNA processing, represent new themes in the biology of Sm/Lsm 
proteins. Moreover this structure has important consequences for snRNP assembly 
that is mediated by two complexes containing the PRMT5 methyltransferase and the 
SMN (survival of motor neurons) protein, respectively. Finally, the ability to 
alter this polypeptide composition by a small mutation in U7 snRNA forms the 
basis for using modified U7 snRNA derivatives to alter specific pre-mRNA 
splicing events, thereby opening up a new way for antisense gene therapy.