FIG. 1.
Sequence alignment (using the Clustal alignment program) and functional activity of cyclin E2 and cyclin E1. (A) Alignment of full-length human cyclin E2 protein with human cyclin E1 protein. The cyclin box is boxed with an unbroken line, the MRSILL sequence is overlined, and the peptide sequence missing from cyclin E2SV is underlined. The C-terminal PEST sequence motif is outlined with a dashed line, and the CDK consensus threonine phosphorylation site is starred. (B) Clustal alignment of murine cyclin E2 and murine cyclin E1. The cyclin box motif is boxed, and the MRSILL sequence is overlined. (C) Functional complementation of yeast G1 cyclins by human cyclin E2. S. cerevisiae MTY618 has a deletion of the CLN1, CLN2, and CLN3 genes and is kept alive by an integrated GAL-CLN3 gene. On galactose medium, CLN3 is transcribed and the cells live; on glucose, the GAL promoter is shut off and the cells fail to grow. Yeast expressing either human cyclin E1 (Hu CycE1) or human cyclin E2 (Hu CycE2) are able to grow on glucose, while yeast harboring vector alone or the human cyclin E2SV (Hu CycE2sv) fail to grow on glucose.