B family DNA polymerases asymmetrically recognize pyrimidines and purines.
Lund TJ, Cavanaugh NA, Joubert N, Urban M, Patro JN, Hocek M, Kuchta RD. B family DNA polymerases asymmetrically recognize pyrimidines and purines. Biochemistry. 2011 Aug 23; 50(33):7243-50.