U4 spliceosomal RNA

The U4 small nuclear Ribo-Nucleic Acid (U4 snRNA) is a non-coding RNA component of the major or U2-dependent spliceosome – a eukaryotic molecular machine involved in the splicing of pre-messenger RNA (pre-mRNA).

The putative U4/U6 snRNA base pairing secondary structure shown in Figure 2., is conserved across a diverse set of organisms suggesting the splicing machinery's ancient origins.

[18] It has been shown previously that a highly conserved Kinked-loop participates in specific protein interactions.

[9][20][21] A cycle has been proposed including both Brr2 as well as the protein prp24 which selectively re-anneals U4 to the U6 snRNA.

[21][22][23][24] A ring of Sm proteins surround a conserved region of the U4 snRNA near the 3' end which are expected to promote favorable interactions between the different snRNPs as well as possibly protect the U4 snRNA from degradation by RNAse enzymes.

A 3D representation of a fragment of a U4 snRNA. The crystal structure of the spliceosomal 15.5KD protein is bound to a U4 snRNA fragment. [ 1 ]
Figure 1. Naked U4 putative secondary structure.
Figure 2. Putative U4/U6 base pairing secondary structure.