The ‘destruction box’ of cyclin A allows B-type cyclins to be ubiquitinated, but not efficiently destroyed.

Abstract

The destruction of mitotic cyclins by programmed proteolysis at the end of mitosis is an important element in cell cycle control. This proteolysis depends on a conserved motif of nine residues known as the ‘destruction box’, which is located 40–50 residues from the N‐terminus. The sequences of the A‐ and B‐type destruction boxes are slightly different, which might account for the differences in timing of their destruction. When the cyclin A‐type destruction box was substituted for the normal one in cyclin B1 or B2, however, the resulting constructs were unexpectedly stable, although the converse substitution of B‐type destruction boxes in cyclin A permitted normal degradation. We compared the ubiquitination of various cyclin constructs, and found that whereas mutation of the highly conserved residues in the destruction box strongly reduced the level of ubiquitinated intermediates, the stable destruction box ‘swap’ constructs did form such adducts. Thus, while ubiquitination is probably necessary for cyclin destruction, it is not sufficient. We also found that poly‐ubiquitinated cyclin derivatives are still bound to p34cdc2, which is not detectably ubiquitinated itself, raising the questions of how cyclin and cdc2 dissociate from one another, and at what stage, in the process of degradation.

The N-terminal Regulatory Domain of Cyclin A Contains Redundant Ubiquitination Targeting Sequences and Acceptor Sites

“…A similar conclusion was obtained with fusion of Xenopus cyclin A1 and cyclin B. 28 This raises an interesting point because one argument for the difficulty in identifying a receptor protein for the D-box is that as soon as the putative protein binds, the D-box-containing protein is rapidly degraded. This should not matter for cyclin A's D-box as fusion proteins appeared to be relatively stable.…”

“…Similarly, cyclin A-cyclin B fusion proteins are stable but are still ubiquitinated. 28 In the absence of the three lysine residues, ubiquitination may shift to other sites. We have not attempted to identify these non-physiological cryptic sites.…”

“…It was shown that substituting the D-box of Xenopus cyclin B with that from cyclin A renders cyclin B non-degradable, whereas the D-box of cyclin B supports the proteolysis of cyclin A. 27,28 In human cells, the D-box of cyclin A is not sufficient for targeting cyclin A for destruction, and an additional short sequence following it (the extended D-box) is also required. 9,10 A similar extended D-box is present in another APC/C substrate NEK2A.…”

Isolation of Trypanosoma brucei CYC2 andCYC3 Cyclin Genes by Rescue of a Yeast G1Cyclin Mutant

“…One difference is that the putative destruction box of CYC3 is located near the C terminus of the protein (Fig. 2), whereas the destruction box in CLB1-4 and in the mammalian A-and B-type cyclins is located at the N terminus (12,70). However, the position of the destruction box is not important, as fusion proteins with the destruction box at various positions are all degraded in a similar way (12,46).…”

APOLLON Protein Promotes Early Mitotic CYCLIN A Degradation Independent of the Spindle Assembly Checkpoint

“…Therefore, CYCLIN B degradation is strictly held in check until the SAC is satisfied. The D-box of CYCLIN B promotes proteasomal degradation in the metaphase when it is grafted onto heterologous proteins (10,24,25), indicating the crucial role of the D-box in the SAC-dependent protein degradation.…”