Isolation and characterization of human orthologs of yeast CCR4-NOT complex subunits

The yeast CCR4-NOT protein complex is a global regulator of RNA polymerase II transcription. It is comprised of yeast NOT1 to NOT5, yeast CCR4 and add itional proteins like yeast CAF1. Here we report the isolation of cDNAs enc oding human NOT2, NOT3, NOT4 and a CAF1-like factor, CALIF, Analysis of the ir mRNA levels in different human tissues reveals a common ubiquitous expre ssion pattern. A multitude of two-hybrid interactions among the human cDNAs suggest that their encoded proteins also form a complex in mammalian cells . Functional conservation of these proteins throughout evolution is support ed by the observation that the isolated human NOT3 and NOT4 cDNAs can parti ally complement corresponding not mutations in yeast. Interestingly, human CALIF is highly homologous to, although clearly different from, a recently described human CAF1 protein. Conserved interactions of this factor with bo th NOT and CCR4 proteins and co-immunoprecipitation experiments suggest tha t CALIF is a bona fide component of the human CCR4-NOT complex.