Background: Dicer is a ribonuclease required for microRNA biogenesis. Results: The two related Dicer enzymes from the thermophilic fungus Sporotrichum thermophile have distinct functions in RNA processing. Conclusion: The helicase domains from each Dicer define the RNA substrate specificity and have distinct RNA binding and ATP hydrolytic activities. Significance: A regulatory function for the helicase domain is conserved from fungi to humans.

Brr2 is a member of the DExD/H family of RNA-dependent ATPases that unwinds the extensively base paired U4/U6 snRNAs during pre-mRNA splicing. This reaction is stimulated by the C-terminus of another spliceosomal protein, Prp8. Prp8 has been shown to bind between Brr2's tandem repeat of