Small Nuclear RNA - U1 SnRNA

U1 SnRNA

U1 snRNP is the initiator of spliceosomal activity in the cell by base pairing with the hnRNA. In the major spliceosome, experimental data has shown that the U1 snRNP is present in equal stoichiometry with U2, U4, U5, and U6 snRNP. However, U1 snRNP's abundance in human cells is far greater than that of the other snRNPs. Through U1 snRNA gene knockdown in HeLa cells, studies have shown the U1 snRNA holds great importance for cellular function. When U1 snRNA genes were knocked out, genomic microarrays showed an increased accumulation of unspliced pre-mRNA. In addition, the knockout was shown to cause premature cleavage and polyadenylation primarily in introns located near the beginning of the transcript. When other uridine based snRNAs were knocked out, this effect was not seen. Thus, U1 snRNA–pre-mRNA base pairing was shown to protect pre-mRNA from polyadenylation as well as premature cleavage. This special protection may explain the overabundance of U1 snRNA in the cell.