  Linguistic analysis of protein sequences is an underexploited technique.
Here, we capitalize on the concept of the lipogram to characterize sequences at
the proteome levels. A lipogram is a literary composition which omits one or
more letters. A protein lipogram likewise omits one or more types of amino
acid. In this article, we establish a usable terminology for the decomposition
of a sequence collection in terms of the lipogram. Next, we characterize
Uniref50 using a lipogram decomposition. At the global level, protein lipograms
exhibit power-law properties. A clear correlation with metabolic cost is seen.
Finally, we use the lipogram construction to differentiate proteomes between
the four branches of the tree-of-life: archaea, bacteria, eukaryotes and
viruses. We conclude from this pilot study that the lipogram demonstrates
considerable potential as an additional tool for sequence analysis and proteome
classification.
