Comparison of human CAP and CAP2, homologs of the yeast adenylyl cyclase-associated proteins

We previously reported the identification of human CAP, a protein that is related to the Saccharomyces cerevisiae and Schizosaccharomyces pombe adenylyl cyclase-associated CAP proteins. The two yeast CAP proteins have similar functions: the N-terminal domains are required for the normal function of adenylyl cyclase, while loss of the C-terminal domains result in morphological and nutritional defects that are unrelated to the cAMP pathways. We have amplified and cloned cDNAs from a human glioblastoma library that encode a second CAP-related protein, CAP2. The human CAP and CAP2 proteins are 64% identical. Expression of either human CAP or CAP2 in S. cerevisiae cap^- strains suppresses phenotypes associated with deletion of the C-terminal domain of CAP, but does not restore hyper-activation of adenylyl cyclase by RAS2(va119). Similarly, expression of either human CAP or CAP2 in S. pombe cap^- strains suppresses the morphological and temperature-sensitive phenotypes associated with deletion of the C-terminal domain of CAP in this yeast. In addition, expression of human CAP, but not CAP2, suppresses the propensity to sporulate due to deletion of the N-terminal domain of CAP in S. pombe. This latter observation suggests that human CAP restores normal adenylyl cyclase activity in S. pombe cap^- cells. Thus, functional properties of both N-terminal and C-terminal domains are conserved between the human and S. pombe CAP proteins.