The Ski complex is a multi-

protein complex A protein complex or multiprotein complex is a group of two or more associated polypeptide chains. Protein complexes are distinct from multidomain enzymes, in which multiple active site, catalytic domains are found in a single polypeptide chain. ...

involved in the

3' end Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. In a single strand of DNA or RNA, the chemical convention of naming carbon atoms in the nucleotide pentose-sugar-ri ...

degradation of

messenger RNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...

s in yeast.

Structure

The complex consists of three main

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s, the RNA

helicase Helicases are a class of enzymes that are vital to all organisms. Their main function is to unpack an organism's genetic material. Helicases are motor proteins that move directionally along a nucleic double helix, separating the two hybridized ...

''Ski2'' and the proteins ''Ski3'' and ''Ski8''. This tetramer contains a 370 kDa core complex, containing N-terminal arms and C-terminal arms from ''Ski3''. The helicase core of ''Ski2'' is positioned by both the C-terminal of ''Ski3'' and two subunits of ''Ski8''.

Mechanism

Helicase activities are initiated by the N-terminal arm and the ''Ski2'' insertion domain. In yeast, the complex guides RNA molecules to the

exosome complex The exosome complex (or PM/Scl complex, often just called the exosome) is a multi-protein intracellular complex capable of degrading various types of RNA (ribonucleic acid) molecules. Exosome complexes are found in both eukaryotic cells and ar ...

for degradation via a fourth protein, called ''Ski7'', which contains a

GTPase GTPases are a large family of hydrolase enzymes that bind to the nucleotide guanosine triphosphate (GTP) and hydrolyze it to guanosine diphosphate (GDP). The GTP binding and hydrolysis takes place in the highly conserved P-loop "G domain", a ...

-like protein. ''Ski7'' involves the 3’ to 5’ degradation of RNA through two different pathways, 3’ poly(A) tail shortening and the binding of the ''Ski2'', ''Ski3'', and ''Ski8'' tetramer and the exosome. Degradation of the 3' mRNA overhang occurs by association with the 80s ribosome. The 3' end of the mRNA is threaded through the ribosome to ''Ski2'', preparing it for the degradation process. Biochemical studies also show that the Ski complex can thread

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

through the exosome complex, thereby coupling the Ski2 protein helicase function with the exoribonuclease activity, leading to degradation of the

strand.

References

{{reflist Protein complexes Gene expression Saccharomyces cerevisiae genes

Structure

Mechanism

See also

References