E3 ubiquitin ligases play key roles in determining the substrate specificity of ubiquitination.U-box E3 ligases have diverse functions in eukaryotes, with a typical U-box domain of 70 amino acids that is present in proteins from yeast to humans.In plants, U-box E3 ligases comprise a large gene family represented by 64 member in Arabidopsis and 77 in rice.These plant U-box (PUB) proteins have been revealed participating in plant developmental processes and environmental responses.However, detailed studies on U-box genes in the model microalgae Chlamydomonas reinhardtii is still lacking to date.Here, a comprehensive analysis of the genes encoding U-box family in C.reinhardtii was performed.After Blastp analysis, 30 full-length U-box genes were identified in C.reinhardtii genome sequence.