SfaNI digestion of the 168-bpFcγRIIIB-NA2–specific gDNA fragment containing the SH mutation at nucleotide position 266. SfaNI recognizes a 5′-GATGC-3′ sequence, which is only present in theFcγRIIIB-SH gene. Lane 1 shows digestion of a fragment amplified from a plasmid containing SH-FcγRIIIb–encoding cDNA, confirming that complete digestion is obtained by Sfa NI treatment. DNA fragments from NA(1+,2+)SH(−) individuals were not digested (lanes 2 through 4), whereas an additional band of 137 bp is visible after digestion of fragments from SH(+) individuals (lanes 5 through 7).