Regulation of Translation Initiation mRNA level

mRNA level control

multiple start codons

upstream ORFs

An mRNA that

has multiple AUGs near the 5’ end can encode different versions of the same protein

A short upstream open reading frame

can regulate translation

short uORF 1

usually, the AUG closest to the 5’ end will be used, in this case making a short non-functional peptide

short uORF 2

occasionally, the first AUG will be skipped and this downstream AUG will be found. A longer protein will be made instead

Regulation of protein synthesis via a uORF

Example: amino acid synthesis regulation in yeast 5’

when amino acids are low, aa-tRNAs are low, and initiation is inefficient low amino acid concentration favors skipping which makes synthesis of the long protein more likely

when amino acids are abundant, aa-tRNAs are abundant, and translation initiation is efficient at the upstream ORF translation of the longer protein is rare