What is a Leaky Scanning

Leaky scanning is a phenomenon in which a weak initiation codon triplet on mRNA is sometimes skipped by ribosome in translation initiation. The 40S ribosomal subunit continues scanning to further initiation codon. The weak initiation codon can be an ACG, or an ATG in a weak Kozak consensus context. This way a mRNA can encode for several different proteins if the AUG are not in frame, or for proteins with different N-terminus if the AUG are in the same frame. Upstream ORFs (uORF) are small coding regions preceding an ORF, The latter must be translated by leaky scanning or termination-reinitiation. Many eukaryotic genes encode for uORF to downregulate the translation/mRNA ratio of a gene. These genes are described in the uORF database The leaky scanning is favored in case of cellular stress in which EIF2alpha is phosphorylated , like in case of dsRNA/PKR activation. Many eukaryotic stress response genes are under the transcription control of a uORF. Viruses may use this regulatory system for their own purpose. #VIRUS #genome #genetics #rybosome #mRNA #viroid