The EMBO Journal, vol. 11, no. 3, presents a study on the role of cyclin A in the human cell cycle. The research shows that cyclin A is essential at two distinct stages: during DNA synthesis (S phase) and entry into mitosis (G₂ phase). Cyclin A interacts with both cdk2 and cdc2, generating two distinct kinase activities. These findings suggest that cyclin A plays a key role in regulating the human cell cycle. The study demonstrates that anti-cyclin A antibodies inhibit DNA synthesis and entry into mitosis when injected into human cells. This inhibition is most effective during the G₁ phase, but less so in S phase. The results indicate that cyclin A is required for both S phase progression and G₂ phase entry. Cyclin A is also involved in the activation of the cdc2-cyclin B complex, which is essential for mitosis. The study further shows that cyclin A is associated with the E2F transcription factor and that this complex is dissociated by the E1A oncogene product. These findings suggest that cyclin A is a target for oncogenic signals. The research also highlights the importance of cyclin A in cell cycle regulation, as its function is required for both S and G₂ phases. The study provides evidence that cyclin A is involved in the activation of the cdc2-cyclin B complex, which is essential for mitosis. The study also shows that cyclin A is involved in the regulation of DNA replication and that its function is required for the progression of the cell cycle. The research demonstrates that cyclin A is essential for the activation of the cdc2-cyclin B complex, which is necessary for mitosis. The study also shows that cyclin A is involved in the regulation of the cell cycle, as its function is required for both S and G₂ phases. The research provides evidence that cyclin A is involved in the activation of the cdc2-cyclin B complex, which is essential for mitosis.The EMBO Journal, vol. 11, no. 3, presents a study on the role of cyclin A in the human cell cycle. The research shows that cyclin A is essential at two distinct stages: during DNA synthesis (S phase) and entry into mitosis (G₂ phase). Cyclin A interacts with both cdk2 and cdc2, generating two distinct kinase activities. These findings suggest that cyclin A plays a key role in regulating the human cell cycle. The study demonstrates that anti-cyclin A antibodies inhibit DNA synthesis and entry into mitosis when injected into human cells. This inhibition is most effective during the G₁ phase, but less so in S phase. The results indicate that cyclin A is required for both S phase progression and G₂ phase entry. Cyclin A is also involved in the activation of the cdc2-cyclin B complex, which is essential for mitosis. The study further shows that cyclin A is associated with the E2F transcription factor and that this complex is dissociated by the E1A oncogene product. These findings suggest that cyclin A is a target for oncogenic signals. The research also highlights the importance of cyclin A in cell cycle regulation, as its function is required for both S and G₂ phases. The study provides evidence that cyclin A is involved in the activation of the cdc2-cyclin B complex, which is essential for mitosis. The study also shows that cyclin A is involved in the regulation of DNA replication and that its function is required for the progression of the cell cycle. The research demonstrates that cyclin A is essential for the activation of the cdc2-cyclin B complex, which is necessary for mitosis. The study also shows that cyclin A is involved in the regulation of the cell cycle, as its function is required for both S and G₂ phases. The research provides evidence that cyclin A is involved in the activation of the cdc2-cyclin B complex, which is essential for mitosis.