Practice question

Pyrrolysine incorporation displays narrow phylogenetic distribution, predominantly encountered in methanogenic Euryarchaeota such as Methanosarcina barkeri, Methanococcus, Methanomassiliicoccales, and few anaerobic Gram-positive bacteria including Desulfitobacterium hafniense, Acetohalobium arabaticum, Thermincola. These organisms utilize methylated amines as methanogenesis substrates, requiring monomethylamine, dimethylamine, trimethylamine methyltransferases harboring pyrrolysine at catalytic site for methyl group transfer to corrinoid proteins. Genes pylTSBCD cluster in operon regulated by methylamine presence. Eukaryotes and majority bacteria lack pyl machinery, terminating translation at UAG. Evolutionary analyses suggest horizontal gene transfer disseminated pyrrolysine system among anaerobes sharing niches rich in methylamines conferring selective advantage.