A nucleotide substitution in a Bg1 II site is responsible for the RFLP discrimination between DPw4 and DPa.

In a previous work we showed that the two functionally different specificities DPw4 and DPa could only be differentiated by RFLP analysis using two mutually exclusive fragments (respectively, Bg1 II 5.29 kb for DPw4 and 7.24 kb for DPa). The DP Workshop synthetic analysis localized these fragments in the DPA2 pseudogene region. Our results demonstrate, however, that they are located between the A1 and B1 genes; the Bg1 II restriction site responsible for the 5.29 kb fragment was localized between the first and second exon of the DPB1 gene and inside the 7.24 kb fragment. A single mutation point inside this restriction site is responsible for the absence of the 5.29 kb fragment, changing the specificity attributed by RFLP typing.