DISRUPTION OF BASE-PAIRING BETWEEN THE 5' SPLICE-SITE AND THE 5' END OF U1 SNRNA IS REQUIRED FOR SPLICEOSOME ASSEMBLY

A short RNA oligonucleotide comprising the 51 splice site consensus se quence (5'SS RNA) is sufficient to bind U1 small nuclear ribonucleopro tein particle (snRNP) or to induce the association of U2 snRNP and U4- U5-U6 triple snRNP. Analysis of the requirements of these interactions demonstrates that the 5'SS RNA is recognized independently by at leas t two different elements during spliceosome assembly: the 51 end of U1 snRNA and a component(s) of the U2-U4-U5-U6 snRNP complex. Since stab le 5'SS RNA-U1 snRNA base pairing prevents interaction of the 5SS RNA with U2-U4-U5-U6 snRNP complex, we conclude that disruption of the ini tial base pairing between the 5'SS RNA and the 5' end of U1 snRNA is r equired for subsequent spliceosome assembly.