Alternatively spliced cyclin C mRNA is widely expressed, cell cycle regulated, and encodes a truncated cyclin box.
The cyclin C protein has recently been shown to associate with a unique cyclin dependent protein kinase (cdk8) and it has been proposed that this complex may regulate RNA transcription during the cell cycle. In addition, the human cyclin C gene has been localized to human chromosome 6q21 and it was found to be frequently deleted in a subset of acute lymphoblastic leukemias (ALL's). Screening of an avian T-cell cDNA library resulted in the isolation of a cyclin C homologue as well as an abundant, yet distinct, cyclin C-related cDNA. The predicted open reading frame (ORF) of the cyclin C cDNA predicted a 283 amino acid protein that was > 99% identical to the human protein and 72% identical to the Drosophila melanogaster protein. However, the predicted ORF of the cyclin C-related cDNA predicted a much smaller 105 amino acid protein that was identical to cyclin C well into the cyclin-box region (amino acid residue 98), where it abruptly diverges and then terminates. Using PCR analysis of cDNA derived from a range of cell lines and tissues, alternative splicing of the avian cyclin C gene has been demonstrated. Furthermore, a smaller approximately 19 kDa protein that co-migrates with the in vitro transcribed and translated truncated cyclin C protein was detected in normal and virally-transformed avian cells with a cyclin C-specific antibody. Expression of alternatively spliced cyclin C mRNA and protein is regulated in a cell cycle-dependent manner reminiscent of cyclin B2. The function of this truncated cyclin C protein is not known, but its expression in avian cells suggest that this truncated cyclin C protein may participate as an early endogenously encoded cyclin C inhibitor.
Li
H
H
Department of Tumor Cell Biology, St Jude Children's Research Hospital, Memphis, Tennessee 38101, USA.
Lahti
J M
JM
Kidd
V J
VJ
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle / Q000235:genetics*; D002460:Cell Line; D002645:Chickens; D003001:Cloning, Molecular; D056745:Cyclin C; D016213:Cyclins / Q000235:genetics*; D018076:DNA, Complementary; D006801:Humans; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D012333:RNA, Messenger / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
C503674:CCNC protein, human; C503678:CycC protein, Drosophila; D056745:Cyclin C; D016213:Cyclins; D018076:DNA, Complementary; D012333:RNA, Messenger