Regulation at Translation Level
Information about translational control in eukaryotes is coming from experiments designed to answer following questions regarding the mechanism of operation of translational machinery.
(i) When there are more than one AUG codons in a mRNA molecule, how does the ribosome know, which one to use for initiation of translation ? (ii) What determines the frequency with which a particular mRNA message is read ? (iii) After finishing translation of an open reading frame (ORF), can a ribosome start again, if an AUG codon follows in the same mRNA within a reasonable length ? (iv) Can a mRNA remain untranslated in a cell and translated only when necessary ?
It has been possible to determine the nucleotide sequence of natural mRNA, to alter these mRNAs as desired and to make synthetic mRNA using recombinant DNA methods. These techniques helped in answering some of the above questions and also yielded information regarding regulation of gene expression at the level of translation. This has partly been discussed in Expression of Gene : Protein Synthesis 4. Translation in Prokaryotes and Eukaryotes
, while describing Kozak's scanning hypothesis
for reading of mRNA by ribosomes in eukaryotes.