Table 2 Functional and structural parallels between CASS and eukaryotic RNAi machinery

Dicers

Helicase/RNAseIII. Processing of long dsRNA into siRNA and pre-miRNA into miRNA, involves unwinding

Helicase (COG1203) + HD nuclease (COG2254) - fused or adjacent genes,

SFII helicase + HD nuclease

Argonautes/slicers

Ferredoxin-fold-PAZ-PIWI – endonuclease, target degradation

RecB-family nuclease (COG1468, 4343); COG1857 – a novel nuclease?

Target degradation

R2D2/RDE-4

dsRNA-binding domain, interacts with Dicer

RAMPs

Ferredoxin-fold duplication. Size-specific psiRNA-binding, pre-psiRNA-binding, other RNA-binding functions?

Fmr1/Fxr

RGG, KH-ssRNA-binding

RAMPs

Ferredoxin-fold duplication. Size-specific psiRNA-binding, pre-psiRNA-binding, other RNA-binding functions?

Tsn

Tudor, SN – RNA-binding

RAMPs

Ferredoxin-fold duplication. Size-specific psiRNA-binding, pre-psiRNA-binding, other RNA-binding functions?

Vig

RGG – RNA-binding

RAMPs

Ferredoxin-fold duplication. Size-specific psiRNA-binding, pre-psiRNA-binding, other RNA-binding functions?

RNA-dependent RNA polymerase

RdRp domain related to DdRp; 2^nd-strand synthesis for siRNA production

Predicted RdRp/RT (COG1353)

Palm polymerase domain. 2^nd strand synthesis for psiRNA production, reverse transcription for CRISPR formation