- Gene amplification of the Menkes (MNK; ATP7A) P-type ATPase gene of CHO cells is associated with copper resistance and enhanced copper efflux. Camakaris, J., Petris, M.J., Bailey, L., Shen, P., Lockhart, P., Glover, T.W., Barcroft, C., Patton, J., Mercer, J.F. Hum. Mol. Genet. (1995)