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Human CDC23: cDNA cloning, mapping to 5q31, genomic structure, and evaluation as a candidate tumor suppressor gene in
1Department of Medicine, University of Chicago, Chicago, Illinois, 60637, USA.
Abstract:
The transition from metaphase to anaphase and exit from mitosis involve the degradation of active cyclin B-CDC2 complexes by ubiquitin-mediated proteolysis. The anaphase-promoting complex (APC) catalyzes the formation of cyclin B-ubiquitin conjugates, thereby targeting cyclin B for degradation. The APC is composed of eight proteins, including four members of a family characterized by multiple tetratricopeptide repeats (TPR). We mapped two overlapping expressed sequence tag clones within a genomic contig on human chromosome 5, band q31. A search revealed high homology to Saccharomyces cerevisiae CDC23, a TPR protein component of the APC. We have isolated the human CDC23 cDNA containing the full-length predicted open reading frame. The approximately 3.3-kb message is ubiquitously expressed and encodes a protein with 591 amino acids (MW = 68,293 Da) and 9 TPR units. The protein has 30% identity and 51% similarity to the S. cerevisiae protein. The human CDC23 gene contains 16 exons and spans approximately 31 kb. CDC23 maps within the smallest commonly deleted segment in myeloid leukemias characterized by a deletion of 5q; however, we detected no mutations of CDC23 in leukemia cells with loss of 5q. Thus, CDC23 is unlikely to be involved in the pathogenesis of myeloid leukemias characterized by abnormalities of chromosome 5.
Insights
The anaphase-promoting complex (APC) targets cyclin B for degradation during mitosis exit. Researchers identified human CDC23, a key APC component, but found no mutations in myeloid leukemias with 5q deletions.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Mitotic exit involves cyclin B-CDC2 complex degradation via ubiquitin-mediated proteolysis.
- The anaphase-promoting complex (APC) orchestrates cyclin B ubiquitination and degradation.
- APC function relies on multiple protein subunits, including those with tetratricopeptide repeats (TPR).
Purpose of the Study:
- To identify and characterize the human CDC23 gene, a TPR-containing component of the APC.
- To investigate the role of human CDC23 in myeloid leukemias with 5q deletions.
Main Methods:
- Expressed sequence tag (EST) mapping to human chromosome 5q31.
- cDNA isolation and sequencing of human CDC23.
- Gene structure analysis (exons, size).
- Homology comparison with Saccharomyces cerevisiae CDC23.
- Mutation analysis in leukemia cell lines.
Main Results:
- Human CDC23 cDNA isolated, encoding a 591-amino acid protein with 9 TPR units.
- Human CDC23 exhibits 30% identity and 51% similarity to its yeast counterpart.
- The human CDC23 gene spans ~31 kb and contains 16 exons.
- CDC23 maps to a commonly deleted region in 5q myeloid leukemias, but no mutations were found in these cells.
Conclusions:
- Human CDC23 is a ubiquitously expressed APC component with conserved structure and function.
- CDC23 is unlikely to be the causative gene in myeloid leukemias with 5q deletions, despite its location.