Table 1.

Molecular characterization of three PNP mutants

Strain	Allele	Erythrocytic PNP activity*	Mutation site	Codon change	Residue	Amino acid substitution	Restriction site
C57BL/6J	Npb	41.0 ± 3.1
B6-NPE	Npb-m260	1.89 ± 0.11	260	ATG to AAG	87	Met → Lys	NdeI (−)
B6-NPF	Npb-m682	0.58 ± 0.05	682	GCA to ACA	228	Ala → Thr	MaeIII (+)
B6-NPG	Npb-m46	0.42 ± 0.20	46	TGG to CGG	16	Trp → Arg	Fnu4HI (+)

The mutation sites are given relative to the initiation of translation. Each mutation resulted in the loss (−) or gain (+) of a restriction enzyme site. 

^*PNP activity is expressed in nanomoles per minute per milligram of protein as the mean ± SD for three to eight mice.