Altered Activity, Social Behavior, and Spatial Memory in Mice Lacking the NTAN1p Amidase and the Asparagine Branch of the N-End Rule Pathway

Abstract

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. N-terminal asparagine and glutamine are tertiary destabilizing residues, in that they are enzymatically deamidated to yield secondary destabilizing residues aspartate and glutamate, which are conjugated to arginine, a primary destabilizing residue. N-terminal arginine of a substrate protein is bound by theUbr1-encoded E3α, the E3 component of the ubiquitin-proteasome-dependent N-end rule pathway. We describe the construction and analysis of mouse strains lacking the asparagine-specific N-terminal amidase (Nt^N-amidase), encoded by the Ntan1 gene. In wild-type embryos,Ntan1 was strongly expressed in the branchial arches and in the tail and limb buds. The Ntan1^−/− mouse strains lacked the Nt^N-amidase activity but retained glutamine-specific Nt^Q-amidase, indicating that the two enzymes are encoded by different genes. Among the normally short-lived N-end rule substrates, only those bearing N-terminal asparagine became long-lived in Ntan1^−/− fibroblasts. TheNtan1^−/− mice were fertile and outwardly normal but differed from their congenic wild-type counterparts in spontaneous activity, spatial memory, and a socially conditioned exploratory phenotype that has not been previously described with other mouse strains.