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 c ...
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 p ...
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 residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
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, separatin ...
''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 pro ...
-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
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 ...
strand.
See also
*
TRAMP complex TRAMP complex (Trf4/Air2/Mtr4p Polyadenylation complex) is a multiprotein, heterotrimeric complex having distributive polyadenylation activity and identifies wide varieties of RNAs produced by polymerases. It was originally discovered in ''Saccharo ...
*
Non-stop decay
Non-stop decay (NSD) is a cellular mechanism of mRNA surveillance to detect mRNA molecules lacking a stop codon and prevent these mRNAs from translation. The non-stop decay pathway releases ribosomes that have reached the far 3' end of an mRNA and ...
*
Nonsense mediated decay
Nonsense-mediated mRNA decay (NMD) is a surveillance pathway that exists in all eukaryotes. Its main function is to reduce errors in gene expression by eliminating mRNA transcripts that contain premature stop codons. Translation of these aberrant ...
References
Protein complexes
Gene expression
Saccharomyces cerevisiae genes
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