Expression and analysis of the rat placental class I cDNA clone encoding the Pa antigen

The previously sequenced cDNA clone pARI.5 was recloned into the mammalian expression vector pcEXV3, and transient and permanent transfectants were prepared in COS7 green monkey kidney fibroblasts. The transfectants were analyzed by indirect immunofluorescence using monoclonal and polyclonal antibodies raised in specifically selected rat strain combinations. These studies showed that pARI.5 encodes the Pa antigen and that the Pa molecule is distinct from the Aa molecule. Probes were derived from the pARI.5 clone and used to study the genomic DNA from Pa-positive and Pa-negative strains. Two probes derived from the 3' untranslated region (3'apARI.5 and 3'bpARI.5) and one probe derived from the 5' region (5'pARI.5) hybridized nonspecifically in all strains under moderate stringency conditions. By contrast, an Xba I restriction fragment unique to the Pa gene was detected with the 5'pARI.5 probe under high stringency conditions. This probe hybridized with a 1.8 kilobase (kb) fragment in the Pa-positive strains and with a 1.7 kb band in the Pa-negative strains. These studies suggest that the gene encoding the Pa antigen, or a fragment thereof, is present in both Pa-positive and Pa-negative strains but may not be expressed in the latter.