Acts as component of the CCR4-NOT core complex, which in the nucleus seems to be a general transcription factor, and in the cytoplasm the major mRNA deadenylase involved in mRNA turnover. The NOT protein subcomplex negatively regulates the basal and activated transcription of many genes. Preferentially affects TC-type TATA element-dependent transcription. Could directly or indirectly inhibit component(s) of the general transcription machinery. Forms a NOT protein complex that comprises NOT1, NOT2, NOT3, NOT4 and NOT5. Subunit of the 1.0 MDa CCR4-NOT core complex that contains CCR4, CAF1, NOT1, NOT2, NOT3, NOT4, NOT5, CAF40 and CAF130. In the complex interacts with CCR4, POP2, NOT2, NOT4 and NOT5. The core complex probably is part of a less characterized 1.9 MDa CCR4-NOT complex. Present with 4300 molecules/cell in log phase SD medium. Belongs to the CNOT1 family.