part of mRNA 5'-splice site recognition biological_process spliceosomal CC complex formation spliceosomal CC complex biosynthesis GO:0000395 U2-type nuclear mRNA 5'-splice site recognition spliceosomal commitment complex formation Recognition of the intron 5'-splice site by components of the assembling spliceosome. Note that this step represents formation of the Commitment Complex (CC, in yeast) or the E complex (mammalian). U2-type nuclear mRNA 5' splice site recognition nuclear mRNA 5' splice site recognition nuclear mRNA 5'-splice site recognition GO:0000368 spliceosomal E complex formation GO:0000369 spliceosomal E complex biosynthesis spliceosomal commitment complex biosynthesis U12-type nuclear mRNA 5'-splice site recognition U12-type nuclear mRNA 5' splice site recognition mRNA splice site recognition mRNA cis splicing, via spliceosome