The p542 gene encodes an autoantigen that cross-reacts with EBNA-1 of the Epstein Barr virus and which may be a heterogeneous nuclear ribonucleoprotein.

In infectious mononucleosis (IM), anti-EBNA-1 antibodies are produced which cross-react with multiple normal human proteins. The cross-reactions can be inhibited with synthetic peptides representing the glycine/alanine repeat in EBNA-1, which implies that the cross-reactivity is due to anti-gly/ala antibodies that cross-react with host proteins containing configurations like those in the EBNA-1 repeat. Here we report the isolation of five gene fragments from a Raji B lymphocyte cDNA library encoding peptides reactive with autoantibodies in an IM serum. One of these, p542, encodes a glycine rich 28-mer which constitutes its cross-reactive epitope, as shown elsewhere. By Northern blots, p542 was identifiable in three B lymphocyte lines, a T cell line, and an epithelial cell line. In a search of the GenBank for proteins with sequence similarity to p542, we found a high degree of identity with the mid- and 3' terminal regions of the recently published mouse gene, Raly, which encodes a protein with the structure of a heterogeneous nuclear ribonuclear protein (hnRNP). We confirmed by anchored RT-PCR our presumption that the 5' sequences of p542 also have a high degree of identity with Raly, including presence of RNA binding motifs characteristic of hnRNPs. There was also sequence homology with human hnRNP C2. From these observations and our previous studies, we conclude that the autoantigen for one of the cross-reactive autoantibodies generated during immune responses to the Epstein Barr virus, anti-p542, is probably an hnRNP.