THE PRESENCE OF MESSENGER-RNA FOR HLA CLASS-I IN HUMAN PLATELETS AND ITS CAPABILITY FOR PROTEIN-BIOSYNTHESIS

In order to determine whether platelets contain specific messenger RNA encoding for HLA class I molecules, polymerase chain reaction (PCR) w as performed with RNA from different platelet donors. Two amplified 30 0 bp and 2 79 bp cDNA fragments were obtained which encompassed sequen ces from 321 to 620 and from 795 to 1073. The 300 bp fragment encodes exon 2 and exon 3, the 2 79 bp encodes a portion of exon 4, exon 5, ex on 6 and a portion of exon 7. A 300 bp nested PCR product from one don or, that encoded for the highly polymorphic region alpha2, was cloned and sequenced. The resulting nucleotide sequences fitted to the expect ed sequence for HLA B3801 of this donor. Sequence analysis of the 279 bp PCR product demonstrated the presence of exon 5 encoding for the 1 17 bp transmembrane domain. In addition, de novo protein biosynthesis was studied by radioimmunoprecipitation of HLA class I molecules from S-35-methionine metabolically labelled platelet lysates with a monoclo nal antibody (mab) w6/32 specific for a monomorphic epitope on the hea vy chain of HLA class I antigens. Analysis of the immunoprecipitates o n SDS polyacrylamide gel electrophoresis showed a specific band with a pparent molecular weight (M(r)) of 44 kD corresponding to integral mem brane HLA protein. On the basis of these results, we conclude that pla telets contain specific messenger RNA encoding for HLA class I molecul es and have the capability to synthesize the integral HLA membrane pro tein.