snRNA class

snRNA

Maturation

Processed by

Structure

snRNA Sm

U1, U2, U4, U4atac, U5, U7, U11 and U12

Subnuclear structures. They need to leave the nucleus and return to it.

Transcribed by Pol II. It requires the union of general transcript factors, such as TFIIA, TFIIB, TFIIE and TFIIF.

Constituted by a 5′-trimethylguanosine cap, a 3′stem–loop and a hetero-heptameric ring structure -Sm site- proteins binding site.

snRNA Lsm

U6 and U6atac

Only in subnuclear structures-they never leave the nucleus-

Transcribed by Pol III

Constituted by a monomethylphosphate cap and a 3′stem- loop, terminating in a stretch of uridines - proteins binding site.