Which factor is NOT involved in the regulation of the cell cycle?

Histones play a crucial role in the packaging and organization of DNA within the nucleus but are not directly involved in regulating the cell cycle. They function primarily through their involvement in chromatin structure, helping to condense DNA into a manageable form during cell division. While histones are essential for maintaining the integrity and accessibility of the genome, they do not influence the timing or progression of the cell cycle stages.

In contrast, growth factors, cyclins, and intracellular signals are key components in cell cycle regulation. Growth factors trigger signaling pathways that promote cell division and proliferation. Cyclins are proteins that regulate the timing of cell cycle transitions by activating cyclin-dependent kinases (CDKs), which push the cell through different phases of the cycle. Intracellular signals, including checkpoints and various signaling molecules, help to monitor the status of the cell and ensure that conditions are right for cell division, thereby maintaining genomic stability. Together, these elements coordinate to ensure the orderly progression through the cell cycle, while histones remain focused on the structural aspect of DNA management.