 Koreaki Ito

Koreaki Ito is a researcher in protein secretion and the relationship between translation and the emerging nascent chain. With Hitoshi Nakatogawa, he showed that the ribosomal exit tunnel can participate in recognizing the sequence of a growing protein, rather than simply providing a passive passage out of the ribosome.^[ref]

Their SecM study connected two kinds of evidence. An arrest-causing sequence in the nascent chain produced ribosome stalling, while suppressor mutations in 23S ribosomal RNA or ribosomal protein L22 allowed elongation to continue. The altered residues faced the tunnel constriction. This localization supported an interaction between the tunnel and the emerging chain.^[ref]

A simplified experiment illustrates why suppressing a phenotype is informative but does not, by itself, prove a direct physical contact. Compare four combinations: ordinary versus altered SecM, each translated by ordinary versus altered ribosomes. If an altered ribosome restores elongation specifically for the arresting sequence, the result links the two components functionally. A general reduction in translation could instead change the apparent abundance of every product; comparing only one final band would miss that alternative. Spatial information about the changed ribosomal RNA and protein residues adds another constraint. Even then, a suppressor mutation might act by changing a nearby conformation rather than removing a direct contact. The experiment is powerful because genetic and structural evidence constrain one another, while leaving room to test the detailed physical mechanism.