dxbp-1(az121) is a K23N mutation that promotes usage of introns starting in UU when the sequence GUU is present at the 5' end of the intron. az121 was initially identified as able to suppress uncoordination of unc-73(e936) by promoting a cryptic splice site that defines an intron beginning UU. smg-4 mutant background allows for high throughput sequencing to identify frame shifted transcripts since it can move the 5'ss over by 1nt. e936az30 has no phenotype on its own, but it offers two adjacent cryptic 5'ss separated by 1nt. Reference: Suzuki JMNGL, et al. PLoS Genet. 2022 Feb 10;18(2):e1010028. doi: 10.1371/journal.pgen.1010028. PMID: 35143478.