May function as a GTPase-activating protein. May play a role in transmission ratio distortion (TRD) in mouse, in which heterozygous males for t-locus transmit their t-carrying chromosome to 95% or more of their offspring. Highly expressed in testis. Expressed in testis at 7 dpc. Previously thought to be the same gene as Tagap1. These are distinct loci that encode proteins with identical C-termini but each with a unique N-terminus.