 E. Coli K-12 MG1655 gene of unknown function

All gene names that start with an Y such as:appear to be proteins of unknown function.

UniProt for example describes YaaX as "Uncharacterized protein YaaX".

As function is discovered, they then change it to a better name, e.g. to names such as the E. Coli K-12 MG1655 transcription unit thrLABC proteins all of which have a clear name due to threonine.

There are many other y??? as of 2021! Though they do tend to be smaller molecules.