Cloning of rabbit Cct6 and the distribution of the Cct complex in mammalian tissues

Cct6 protein is one of the subunits of the Cct complex involved in ATP-dependent folding of cellular proteins. We used the cDNA of the human CCT6 subunit to obtain a full-length cDNA from a rabbit kidney cortex library. Two transcripts of 2 and 2.5 kb were detected in rabbit kidney and liver by Northern analysis. The rabbit CCT6 was 93% identical to the human gene; the deduced amino acid sequence was 97% identical. A phylogenetic analysis of Cct6 proteins from mouse, rabbit, human, and yeast showed greater similarities of Cct6 protein among the species than among other Cct subunits. The ATP-binding sites were perfectly conserved among mammals and yeast, supporting the role of Cct complex in ATP-dependent protein folding. Using a polyclonal antibody to human Cct6 protein and Western analysis, we found expression of this subunit in a variety of rabbit organs and tissues, as well as in bovine testes, human lymphocytes, human and rabbit reticulocytes, and in two cultured kidney cell lines. We also found Cct1 protein by Western analysis in several rabbit organs as well as in bovine testes. These data characterize the rabbit Cct6 subunit and compare it to its homologues. The Western analyses support the concept that Cct complex is widely distributed among tissues and highly conserved among eukaryotes.