Anti-proliferative protein; the function is mediated by association with deadenylase subunits of the CCR4-NOT complex. Mediates CPEB3-accelerated mRNA deadenylation by binding to CPEB3 and recruiting CNOT7 which leads to target mRNA deadenylation and decay. Interacts with ERBB2 (By similarity). Interacts with CNOT7 (By similarity). Interacts with CPEB3 (via C-terminal RNA-binding region); recruits CNOT7 to CPEB3 to form a ternary complex required for mRNA deadenylation and decay (PubMed:21336257). Interacts with CNOT8 (By similarity). Interacts with CPEB4 (By similarity). Only a small fraction localizes to the cytoplasm except in late S-phase where more than half of proteins become cytoplasmic. Phosphorylated on Ser and Thr residues. Belongs to the BTG family.