Base-pair specificity of the U6 snRNA allows the U6 snRNP to bind tightly to the U4 snRNA and loosely to the U5 snRNA of a triple-snRNP during the initial phase of the splicing reaction.
The association of U6 snRNA with the 5' end of the intron via base-pairing during the splicing reaction occurs prior to the formation of the lariat (or lasso-shaped) intermediate, and is required for the splicing process to proceed.