InterPro domain: IPR039771

This entry includes archaeal exosome complex component Csl4 and its homologues from eukaryotes. In budding yeast, Csl4 is also known as Ski4 due to itssuperkiller (SKI) phenotype first described as a more efficient ability to kill sensitive non-killer yeast strains [ 1 , 2 ]. Later, it was found to be part of the yeast exosome complex involved in 3'-5' RNA processing and degradation in both the nucleus and the cytoplasm [ 3 ].

Csl4 is a non-catalytic component of the exosome, a complex involved in RNA processing and degradation [ 4 , 5 ]. The exact composition of the exosome varies, depending on the organism or the subcellular localization, but in all cases it is composed of a ring-shaped core made of three heterodimers (Rrp41p/Rrp45p, Rrp43p /Rrp46p, Rrp42p/Mtr3p) stabilized by the presence of three other proteins (Csl4/Ski4, Rrp4p, Rrp40p) [ 6 ]. The presence of different proteins in the cap may enable interactions with different substrates. It has been shown that the archaeal DnaG protein needs Csl4 for binding to the exosome. DnaG is a poly(A)-binding protein and enhances the degradation of adenine-rich transcripts by the Csl4-exosome [ 6 ].

1. Yeast killer mutants with altered double-stranded ribonucleic acid. J. Bacteriol. 117, 681-6
2. Yeast RNA viruses as indicators of exosome activity: human exosome hCsl4p participates in RNA degradation in Saccharomyces cerevisiae'. Yeast 28, 821-32
3. Function of the ski4p (Csl4p) and Ski7p proteins in 3'-to-5' degradation of mRNA. Mol. Cell. Biol. 20, 8230-43
4. Structural framework for the mechanism of archaeal exosomes in RNA processing. Mol. Cell 20, 461-71
5. Quantitative analysis of processive RNA degradation by the archaeal RNA exosome. Nucleic Acids Res. 38, 5166-76
6. The archaeal DnaG protein needs Csl4 for binding to the exosome and enhances its interaction with adenine-rich RNAs. RNA Biol 10, 415-24