Structure based Functional Distinction between Cln1 and Cln2 Depends on the Ubiquitin-Proteasome Pathway

Cln1 and Cln2, G1/S cyclins of the ascomycetous budding yeast Saccharomyces cerevisiae (S. cerevisiae), oscillate during the cell cycle, rising in late G1 and falling in early S phase. The researchers have been tried to elucidate the structure basis of the functional distinction between Cln1 and Cln2. In this article, they performed in silico simulations: construction and evaluation of three dimensional structures of Cln1-Cdc28 and Cln2-Cdc28 complexes. They in silico simulations suggested that the interaction of Cln1 and Cln2 with Cdc28 were in the two distinct situations, designated as flip and flop conformation, at the extra amino acid region in the cyclin box of Cln1 and Cln2. They speculated the trigger of this flip-flop conversion of the extra amino acid region in the cyclin box of Cln1-Cdc28 and Cln2-Cdc28 might be regulated by the ubiquitination of the sequences rich in Pro, Glu, Ser and Thr, so-called PEST motifs, in Cln1 and Cln2.