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. 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 NOT1. The core complex probably is part of a less characterized 1.9 MDa CCR4-NOT complex. Present with 1320 molecules/cell in log phase SD medium.