Formation of a quadruple snRNP complex composed of the spliced leader (SL) RNA along with the U4/U6-U5 tri-snRNP complex. Interactions that may facilitate this include a duplex between the SL and U6 RNAs and interactions between the U5 RNA and the exon sequence at the 5' splice site within the SL RNA.
formation of quadruple SL/U4/U5/U6 snRNP