Protein kinase Sut1 from the Crenarchaeon Sulfolobus acidocaldarius displays tyrosine phosphorylation activity

Protein phosphorylation is a key cellular signaling mechanism that exists in all life forms. Unlike Bacteria and Eukarya, in which protein phosphorylation has thoroughly been studied, post-translational modification by means of phosphorylation have only been limitedly explored in Archaea. A previous study of the phosphoproteome of the model Crenarchaeon Sulfolobus acidocaldarius revealed a widespread occurrence of protein phosphorylation, especially on tyrosine residues. Moreover, several (putative) transcription factors, including AbfR1 and FadR, were previously shown to be phosphorylated on tyrosine residues, a phenomenon that is directly linked to a phosphorylation-mediated regulation of these transcription factors. Despite this potentially important role for tyrosine phosphorylation in S. acidocaldarius, to our knowledge, a kinase capable of directly phosphorylating tyrosine residues has not yet been identified in this organism, neither in Archaea as a whole. Here, we identify and characterize a protein kinase in S. acidocaldarius, Sut1, which displays tyrosine phosphorylation activity in vitro and represents a novel protein kinase family that is widespread in different archaeal organisms. ### Competing Interest Statement The authors have declared no competing interest.