Protein sequences conserved in prokaryotic aminoacyl-tRNA synthetases are important for the activity of the processivity factor of human mitochondrial DNA polymerase

Previous studies have shown that the small subunit of Xenopus DNA polymeras e gamma (pol gamma B) acts as a processivity factor to stimulate the 140 kD a catalytic subunit of human DNA polymerase gamma, A putative human pol gam ma B initially identified by analysis of DNA sequence had not been shown to be functional, and appeared to be an incomplete clone. In this paper, we r eport the cloning of full-length human and mouse pol gamma B, Both human an d mouse pol gamma B proteins were expressed in their mature forms, without their apparent mitochondrial localization signals, and shown to stimulate p rocessivity of the recombinant catalytic subunit of human pol gamma A. Dele tion analysis of human pol gamma B indicated that blocks of sequence conser ved with prokaryotic class II aminoacyl-tRNA synthetases are necessary for activity and interaction with human pol gamma A. Purification of DNA pol ga mma from HeLa cells indicated that both proteins are associated in vivo.