Article Abstract:
Xenopus egg extracts show that at least two ubiquitin-conjugating E2 enzymes can complement the anaphase-promoting complex (APC) and ubiquitin-activating enzyme E1 to ubiquitinate cyclin B by a common recognition mechanism. One of the E2 enzymes is a Xenopus homolog of UBC4. The APC is a CDC27- and CDC16-containing 20S complex that determines the cell cycle specificity of cyclin ubiquitination by acting as a cyclin-ubiquitin ligase which degrades cyclin B in mitosis.
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Article Abstract:
Another mechanism of mutant DNA overreplication was seen in the analysis of CDC-mutated strains of Saccharomyces cerevisiae. Mutants of the CDC16 and CDC27 genes showed DNA overreplication in a single cell cycle, either by aberrant mitosis or bypassing mitosis through another G1 or S phase. The two genes are believed to act on an S phase initiator to regulate DNA replication to once every cell cycle.
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Article Abstract:
A formaldehyde cross-linking study revealed that Mcm7p and Cdc6p initiation proteins are specifically associated with Saccharomyces cerevisiae DNA replication origins in G1 but not in G2. Results also show that Mcm7p is dependent on Cdc6p in terms of origin association. Furthermore, the Cdc6p occupancy and S- and M-CDKs were found to regulate the loading of Mcm proteins onto origins.
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