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 multienzyme complexes, in which multiple catalytic domains are found in a single polypeptide chain. Protein ...

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- ...

degradation of messenger RNAs 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 residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

s, the RNA

helicase Helicases are a class of enzymes thought to be 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 acid phosphodiester backbone, separat ...

''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 a ...

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 essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

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

strand.

References

Protein complexes Gene expression Saccharomyces cerevisiae genes {{Biochemistry-stub

Structure

Mechanism

See also

References