Leaky scanning

Leaky scanning is a mechanism used during the initiation phase of eukaryotic translation that enables regulation of gene expression. During initiation, the small 40S ribosomal subunit (as a 43S PIC) "scans" or moves in a 5' --> 3' direction along the 5'UTR to locate a start codon to commence elongation. Sometimes, the scanning ribosome bypasses the initial AUG start codon and begins translation at further downstream AUG start codons.[1] Translation in eukaryotic cells according to most scanning mechanisms occurs at the AUG start codon proximal to the 5' end of mRNA; however, the scanning ribosome may encounter an “unfavorable nucleotide context” around the start codon and continue scanning.[2]

There are certain instances where initiation has been found to occur upstream at a non-AUG codon. Eukaryotic genes containing consistent G-C rich leader sequences are frequently observed performing this mechanism. It is hypothesized that scanning is slowed due to a secondary structure which allows for the binding of Met-tRNA with the mismatch codon.[3]

Several viruses use a leaky scanning mechanism to produce vital proteins which implies that leaky scanning is not a consequence of inadequacy, but instead allows viruses to overcome the high selective pressures of competing with their hosts.[4] Molecular biologists are narrowing the search of the ideal nucleotide environment for initiation of translation, and the mechanisms by which viruses replicate.[1]

  1. ^ a b Kozak, Marilyn. “Initiation of Translation in prokaryotes and eukaryotes.” Gene 234 (1999): 187-208. Academic Search Complete. Web. 10 June 2014.
  2. ^ Herzog, Etienne., et al. “Translation of the Second Gene of Peanut Clump Virus RNA 2 Occurs by Leaky Scanning In Vitro.” Virology 208. (1995): 215-225. Academic Search Complete. Web. 10 June 1014.
  3. ^ Kozak, Marilyn. “Pushing the limits of the scanning mechanism of initiation of translation.” Gene 299 (2002): 1-34. Academic Search Complete. Web. 11 June 2014.
  4. ^ Ryaboba, Lyubov., et al. “Translation reinitiation and leaky scanning in plant viruses.” Virus Research 119 (2006): 52-62 Academic Search Complete. Web. 23 June 2014.