Inhibits translesion DNA synthesis by preventing monoubiquitination of PCNA, this is necessary to counteract damage due to ultraviolet light-induced replication stress (PubMed:27906959). SDE2 is cleaved following PCNA binding, and its complete degradation is necessary to allow S-phase progression following DNA damage (PubMed:27906959). ; Plays a role in pre-mRNA splicing by facilitating excision of relatively short introns featuring weak 3′-splice sites (ss) and high GC content (PubMed:34365507). May recruit CACTIN to the spliceosome (By similarity). ; Plays a role in ribosome biogenesis by enabling SNORD3- and SNORD118-dependent cleavage of the 47S rRNA precursor (PubMed:34365507). Binds ncRNA (non-coding RNA) including the snoRNAs SNORD3 and SNORD118 (PubMed:34365507).