Home Introduction Mechanism U1 U2 U4 U5 Associated Proteins References

U6 snRNP

Discovery

In 1980, a 4.6S RNA was discovered by Yerach Daskal and his research group when they used the Bernhard bleaching procedure to isolate perichromatin graanules (Daskal et. al., 1980; Epstein et. al., 1980). This 4.6 S RNA became known as the U6 snRNA. The same year, the nucleotide sequence of the nuclear U6 (4.7S) RNA was determined by Paul Epstein and his research group by exposing the RNA to various types of enzymatic digestions and gel sequencing techniques (Epstein et. al., 1980). The U4-U6 snRNP complex was discovered in 1984 by Bringmann et. al., as previously noted in the U4 section of this website.

Function

Using two distinct methods, two different research groups headed by Christine Guthrie and Joan Steitz, respectively, concluded that the U6 snRNA assists in the removal of an intron from a pre-mRNA sequence by base pairing with the 5’ end of the intron (Sontheimer et.al, 1993; Lesser et. al, 1993). Steitz and her research group showed that U6 could be crosslinked to the intron at the + 5 position. Steitz suggested that the ACA sequence in the ACAGAC portion of the U6 sequence base pairs with the UGU conserved sequence in the splice sites which are at positions +4, +5 and

+6 (Sontheimer et.al, 1993).

The research group headed by Guthrie showed that base pairing between the ACAGAG sequence of U6 and the 5’ splice site was necessary for the intron to be spliced properly by using genetic experiments on yeast that were performed in vivo. This research group studied mutations in U6 and the intron that were predicted to stabilize the interaction of the two. This led to an increase in the amount of normal cleavage and a decrease in that of aberrant cleavage. This group suggested that the base pairs are formed between positions 4,5 and 6 of the intron to the nucleotides 47, 48 and 49 of U6 (Lesser et. al, 1993).

Both of these studies indicate that U6 assists in the intron splicing process by binding to the 5’ splice site.

Interactions

The research group headed by Robert Roscigno in 1995 found that SR proteins are responsible for bringing the U4/U6*U5 tri snRNP complex to the assembling spliceosome. They determined this by isolating partially purified pre-spliceosomes and following them until they were functional for splicing pre-mRNA in vitro. They established that phosphorylated SR proteins are necessary for the pre-spliceosome to spliceosome transition (Roscigno et.al., 1995).

Home Introduction Mechanism U1 U2 U4 U5 Associated Proteins References