ROLE OF U6 SNRNA IN 5' SPLICE-SITE SELECTION

Two models describing the interaction between U6 small nuclear RNA (sn RNA) and the 5' splice site of introns have been proposed on the basis of cross-linking experiments. Here it is shown that a conserved seque nce present in U6 snRNA forms base pairs with conserved nucleotides at the 5' splice junction and that this interaction is involved in 5' sp lice site choice. These results demonstrate a specific function for U6 snRNA in splicing and suggest that U6 snRNA has a proofreading role d uring splice site selection. A model is presented in which this new in teraction, in concert with previously described interactions between U 6 snRNA, U2 snRNA, and the pre-messenger RNA, would position the branc h point near the 5' splice site for the catalysis of the first splicin g step.