Phosphorylation usually occurs on serine, threonine, tyrosine and histidine residues in eukaryotic proteins. Candidate include aspartate, glutamate, histidine, cysteine. The main amino acids involved are serine, histidine, and aspartic acid. A similar attenuation mechanism regulates the synthesis of histidine, phenylalanine and threonine. In general, zinc fingers coordinate zinc ions with a combination of cysteine and histidine residues. Cytokinin activates histidine kinases which then phosphorylate histidine phosphotransfer proteins. The mutation causes substitution of codon 206 from arginine to histidine in the ACVR1 protein. Histidine and glutamine are alternating peptide tags (HQHQHQ). This gene is an histidine kinase sensor. Besides the URA3 selection one can also use the histidine, leucine and arginine autotrophy. Glycine, histidine, and sarcosine can also directly contribute to the THF-bound 1C pool. The imidazole sidechain of histidine commonly serves as a ligand in metalloproteins. Anionic residues form a pathway facilitating proton movement away from the catalytic histidine. Closantel induces aggregation of the histidine kinase sensor in two-component signalling. The most pervasive is the amino acid histidine, which has an imidazole side-chain.