PC-1 is a membrane glycoprotein expressed selectively on murine antibody-secreting plasma cells. Previously, we have obtained partial amino acid sequence data for this protein. Here, we describe the use of these data in the isolation of PC-1 cDNA clones. To avoid the "3'-bias" of conventional cDNA libraries we constructed a cDNA library in lambda gt10 by priming the first strand of cDNA synthesis with random hexadeoxynucleotides. The library was screened with oligonucleotide probes, 17 nucleotides in length, the design of which was based on the amino acid sequence data. Two cDNA clones of 1.0 and 0.9 kilobase pairs (lambda RR3 and lambda RR20, respectively) were isolated. Both contained a sequence encoding the 15-residue tryptic peptide that was used to derive the sequences of the oligonucleotide probes. lambda RR3 cDNA hybridized to an approximately equal to 3.5-kilobase mRNA that was present in plasmacytomas, spleen, and liver but not in other cell types screened. We were unable to detect PC-1 mRNA or protein in mouse brain. In the spleens of mice chronically infected with Mesocestoides corti, PC-1 mRNA was present at 2.5-fold higher levels than found in normal mouse spleens, whereas immunoglobulin mRNA levels were 15-fold higher. Southern blot analyses revealed the presence of only one gene copy per haploid mouse genome. Restriction fragment length polymorphisms were detected in genomic DNA from mice bearing different PC-1 alleles. A related gene is present in rat genomic DNA.