GO:0002945 cyclin K-CDK13 complex guide

The cyclin K-CDK13 complex (GO:0002945) is a cellular component defined as a protein complex consisting of cyclin K and cyclin-dependent kinase 13 (CDK13). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle, and cyclin-dependent kinases (CDKs) are a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner. This complex therefore represents a functional kinase holoenzyme in which cyclin K serves as the regulatory subunit and CDK13 as the catalytic subunit. Understanding GO:0002945 is important because it provides a precise ontological handle for annotating proteins, interactions, and pathways that converge on this specific kinase module. Researchers studying viral pathogenesis, transcription, and cell-cycle regulation need to distinguish the cyclin K-CDK13 complex from other CDK-cyclin pairs, and GO:0002945 enables that specificity. The term is also relevant for functional genomics: CRISPR screens and interaction proteomics frequently identify cyclin K and CDK13 as hits, and mapping those hits to GO:0002945 helps prioritize mechanistic follow-up. In this article, we synthesize the QuickGO definition with published literature to describe the composition, assembly, molecular mechanism, disease links, and experimental methods for studying the cyclin K-CDK13 complex.

GO:0002945 (cyclin K-CDK13 complex) is a cellular component term describing a protein complex that contains cyclin K and cyclin-dependent kinase 13 (CDK13). The QuickGO definition states that it is a protein complex consisting of cyclin K and CDK13, and it notes that cyclins show periodicity in protein abundance through the cell cycle while CDKs are serine/threonine protein kinases activated by binding to a cyclin partner. The synonym CycK/Cdk13 complex refers to the same entity. In practical terms, GO:0002945 is used to annotate gene products that physically assemble into this two-subunit kinase module, as opposed to free cyclin K or monomeric CDK13.

The cyclin K-CDK13 complex is important because it is a discrete, experimentally tractable kinase module that can be annotated, perturbed, and targeted. Its identification as a host factor co-opted by HIV-1 Nef to antagonize SERINC5 places it at the interface of viral pathogenesis and host restriction. For researchers, GO:0002945 provides a standardized way to describe the complex in functional enrichment analyses, interaction networks, and CRISPR screen results, reducing ambiguity when cyclin K or CDK13 appear as hits.

The following genes and proteins are directly or functionally associated with the cyclin K-CDK13 complex (GO:0002945) based on the verified literature.

The cyclin K-CDK13 complex is regulated at the level of subunit availability and interaction. Cyclins are characterized by periodicity in protein abundance throughout the cell cycle, and CDKs become active upon binding to a cyclin regulatory partner. In the case of GO:0002945, cyclin K serves as the regulatory subunit that enables CDK13 kinase activity. Viral regulation is also documented: HIV-1 Nef interacts with the cyclin K/CDK13 complex to antagonize SERINC5 for optimal viral infectivity, effectively modulating the complex's functional output during infection. Beyond these points, the verified literature does not provide additional mechanistic details on upstream regulators of this specific complex.

The cyclin K-CDK13 complex is directly implicated in HIV-1 biology: HIV-1 Nef interacts with the cyclin K/CDK13 complex to antagonize SERINC5 for optimal viral infectivity. This means the complex functions in a host-pathogen axis where its activity supports viral spread by counteracting a host restriction factor. Experimental models that perturb cyclin K or CDK13 can therefore be used to test whether the complex is required for Nef-dependent SERINC5 antagonism.

SERINC5 is a host restriction factor that limits HIV-1 infectivity, and its antagonism by Nef requires the cyclin K/CDK13 complex. This links GO:0002945 to the broader biology of host defense and viral counter-defense. Researchers studying restriction factors can use the complex as a defined entry point for mechanistic studies.

CDK13 is a cyclin-dependent kinase, and cyclin-CDK complexes are broadly relevant to cell-cycle and transcriptional regulation. While the verified literature for this article focuses on HIV-1 Nef and SERINC5, the annotation of GO:0002945 provides a foundation for future studies exploring whether the complex contributes to proliferative or transcriptional programs in disease.

Because GO:0002945 is defined as a protein complex, co-immunoprecipitation of cyclin K or CDK13 followed by mass spectrometry is a direct way to confirm assembly and identify interacting partners such as HIV-1 Nef. Tagged knock-in cell lines expressing epitope-tagged CCNK or CDK13 enable endogenous-complex purification.

CDK13 is a serine/threonine protein kinase activated by cyclin binding. In vitro kinase assays using immunopurified cyclin K-CDK13 complex can measure catalytic activity and test whether specific mutations in either subunit abolish function.

Knockout of CCNK or CDK13 followed by HIV-1 infectivity assays can test the requirement for the complex in Nef-mediated SERINC5 antagonism. These experiments link the cellular component annotation to a measurable viral phenotype.

Phosphoproteomic profiling of cells with and without the cyclin K-CDK13 complex can identify candidate substrates and downstream signaling changes. This approach helps define the molecular function of the complex beyond its physical composition.

Researchers studying cyclin K-CDK13 complex-related genes often need to determine whether a candidate gene is causally involved in complex assembly, kinase activity, or downstream phenotypes such as viral infectivity. Rigorous causal inference requires well-controlled genetic models that isolate the complex from related cyclin-CDK modules.

The cyclin K-CDK13 complex (GO:0002945) is a defined cellular component consisting of cyclin K and CDK13, with a clear role as a cyclin-activated serine/threonine kinase holoenzyme. Its functional importance is highlighted by the finding that HIV-1 Nef interacts with the complex to antagonize SERINC5 and support viral infectivity. For researchers, GO:0002945 offers a precise annotation that supports mechanistic, genetic, and pharmacological studies of this kinase module. Continued work using CRISPR models, interaction proteomics, and phosphoproteomics will refine our understanding of the complex in health and disease.