Cyclin box fold superfamily; The cyclin box is a protein binding domain that functions in cell-cycle and transcriptional control. It is about 100 amino acids in length, composed of five helices, and is present in cyclins, transcription initiation factor IIB (TFIIB), and retinoblastoma tumour suppressor protein (Rb). Cyclins consist of 8 classes of cell cycle regulators that function as regulatory subunits of cyclin-dependent kinases (CDKs), which are serine/threonine kinases. The catalytic activities of CDKs are modulated not only by their interactions with cyclins but also by CDK inhibitors (CKIs). CDKs, cyclins and CKIs play key roles in transcription, epigenetic regulation, metabolism, stem cell self-renewal, neuronal functions, and spermatogenesis. TFIIB is a transcription factor that binds the TATA box. Members in this superfamily contain one or two copies of the cyclin box.

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                 ....*....|....*....|....*....|....*....|....*....|
gi 966943267  44 QRDEVIQWLAKLKYQFNLYPETFALASSLLDRFLATVKFH-----AIAVS 88
Cdd:cd20526    1 QRDEAVRWLAELNSQFKFYPETFALAVSILDRFLASVKARpkylrCIAIS 50

cyclin box found in cyclin-I (CCNI) and similar proteins; CCNI is an atypical cyclin because it is most abundant in post-mitotic cells. It is involved in various biological processes, such as cell survival, angiogenesis, cell differentiation, and cell cycle progression. CCNI contains a typical cyclin box near the N-terminus and a PEST sequence near the C-terminus. The cyclin box is a protein binding domain.

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                 ....*....|....*....|....*....|....*....|....*....|
gi 966943267  44 QRDEVIQWLAKLKYQFNLYPETFALASSLLDRFLATVKFH-----AIAVS 88
Cdd:cd20526    1 QRDEAVRWLAELNSQFKFYPETFALAVSILDRFLASVKARpkylrCIAIS 50

Cyclin [Cell division and chromosome partitioning];

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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 966943267  13 SFLLEKAITREAQMwKVNVRKMPSNQNVSPSQRDEVIQWLAKLKYQFNLYPETFALASSLLDRFL 77
Cdd:COG5024  182 SDIFEYLLKLELID-LPNPNYLIKQSLYEWSMRSILVDWLVEVHGKFGLLPETLFLAINIIDRFL 245

cyclin box found in cyclin-I (CCNI) and similar proteins; CCNI is an atypical cyclin because it is most abundant in post-mitotic cells. It is involved in various biological processes, such as cell survival, angiogenesis, cell differentiation, and cell cycle progression. CCNI contains a typical cyclin box near the N-terminus and a PEST sequence near the C-terminus. The cyclin box is a protein binding domain.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|
gi 966943267  44 QRDEVIQWLAKLKYQFNLYPETFALASSLLDRFLATVKFH-----AIAVS 88
Cdd:cd20526    1 QRDEAVRWLAELNSQFKFYPETFALAVSILDRFLASVKARpkylrCIAIS 50

first cyclin box found in cyclin-B1 (CCNB1)-like family; The CCNB1-like family includes two B-type cyclins, CCNB1 and CCNB2, both of which are essential for the control of the cell cycle at the G2/M (mitosis) transition. Members in this family contain two cyclin boxes. This model corresponds to the first one. The cyclin box is a protein binding domain.

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                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 966943267  21 TREAQMwKVNVRKMPSNQNVSPSQRDEVIQWLAKLKYQFNLYPETFALASSLLDRFLATVK 81
Cdd:cd20507   14 QLEKKY-AIDPDYLSGQPEITERMRAILVDWLVEVHLKFKLLPETLYLTVNIIDRYLSKKQ 73

first cyclin box found in yeast B-type cyclins; This subfamily includes Saccharomyces cerevisiae G2/mitotic-specific cyclins 1-4 (ScCLB1-4), S-phase entry cyclins 5-6 (ScCLB5-6), and Schizosaccharomyces pombe G2/mitotic-specific cyclins, cig1, cig2 and cdc13. ScCLB1-4 are essential for the control of the cell cycle at the G2/M (mitosis) transition. They interact with the CDC2 protein kinase to form maturation promoting factor (MPF). ScCLB5-6 interact with CDC28 and are involved in DNA replication in Saccharomyces cerevisiae. ScCLB5 is required for efficient progression through S phase and possibly for the normal progression through meiosis. ScCLB6 is involved in G1/S and or S phase progression. Cig1 is required for efficient passage of the G1/S transition. Cig2 and cdc13 are essential for the control of the cell cycle at the G2/M and G1/S (mitosis) transitions. They interact with the cdc2 protein kinase to form MPF. Members in this family contain two cyclin boxes. This model corresponds to the first one. The cyclin box is a protein binding domain.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|....*
gi 966943267  34 MPSNQNVSPSQRDEVIQWLAKLKYQFNLYPETFALASSLLDRFLA 78
Cdd:cd20568   30 MDDQKELRWKMRGILVDWLVEVHEKFRLLPETLFLAVNIIDRFLS 74

first cyclin box found in Arabidopsis thaliana B-type cyclins (CycBs) and similar proteins; Plant B-type cyclins (CycBs) correspond to a group of G2/mitotic-specific cyclins that are functionally linked to S- and M-phases of the mitotic cycle, which predicts their involvement also in meiosis. CycBs associate with their partner cyclin-dependent kinases (CDKs) to trigger the kinase activity. They contain two cyclin boxes. This model corresponds to the first one. The cyclin box is a protein binding domain.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|....*.
gi 966943267  34 MPSNQ-NVSPSQRDEVIQWLAKLKYQFNLYPETFALASSLLDRFLA 78
Cdd:cd20567   42 YMSQQpDINEKMRAILIDWLIEVHLKFELMPETLYLTVNLIDRFLS 87

first cyclin box found in Arabidopsis thaliana A-type cyclins (CycAs) and similar proteins; Plant A-type cyclins (CycAs) correspond to a group of G2/mitotic-specific cyclins that are functionally linked to S- and M-phases of the mitotic cycle, which predicts their involvement also in meiosis. CycAs associate with their partner cyclin-dependent kinases (CDKs) to trigger the kinase activity. They contain two cyclin boxes. This model corresponds to the first one. The cyclin box is a protein binding domain.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|
gi 966943267  38 QNVSPSQRDEVIQWLAKLKYQFNLYPETFALASSLLDRFL 77
Cdd:cd20562   35 RDITPSMRGILVDWLVEVAEEYKLVPDTLYLTVSYIDRFL 74

domain present in cyclins, TFIIB and Retinoblastoma; A helical domain present in cyclins and TFIIB (twice) and Retinoblastoma (once). A protein recognition domain functioning in cell-cycle and transcription control.

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                   ....*....|....*....|....*....|....*....|....*
gi 966943267    50 QWLAKLKYQFNLYPETFALASSLLDRFLATVKFhaiaVSTRPQLL 94
Cdd:smart00385   1 DFLRRVCKALNLDPETLNLAVNLLDRFLSDYKF----LKYSPSLI 41

first cyclin box found in cyclin-A (CCNA) family; The CCNA family includes two A-type cyclins, CCNA1 and CCNA2. CCNA1 may primarily function in the control of the germline meiotic cell cycle and additionally in the control of mitotic cell cycle in some somatic cells. CCNA2 controls both the G1/S and the G2/M transition phases of the cell cycle. Members in this family contain two cyclin boxes. The model corresponds to the first one. The cyclin box is a protein binding domain.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|....*..
gi 966943267  34 MPSNQNVSPSQRDEVIQWLAKLKYQFNLYPETFALASSLLDRFLATV 80
Cdd:cd20504   24 MRKQPDINPSMRSILVDWLVEVAEEYKLVPETLYLAVNYIDRFLSQM 70