Expression levels of pocket proteins throughout the cell cycle. In G0, the most abundant pocket protein is p130. After cells are stimulated to enter the cell cycle expression of pRB and p107 are induced because they are E2F target genes themselves. At the same time these pocket proteins increase, the expression level of p130 begins to decline. In subsequent cell cycles pRB and p107 remain expressed at relatively constant levels, conversely, p130 is relatively inabundant under these growth conditions. These unique expression patterns offer clear, distinguishing characteristics of each pocket protein family member.