Structure and expression of the genes coding for human alpha 1‐acid glycoprotein.

alpha 1‐acid glycoprotein (alpha AGP) is a well‐characterized human plasma protein. Its structural properties have been studied for many years but little is known about its function. Amino acid sequence analysis of purified human alpha AGP from plasma pooled from several individuals showed considerable heterogeneity. We have cloned the genomic DNA segment encoding alpha AGP and we show that it contains three adjacent alpha AGP coding regions, AGP‐A, B and B‘, identical in exon–intron organization but with slightly different coding potential. These results account for the heterogeneity observed by protein sequencing. Southern blot analysis indicates that the cloned cluster contains all the alpha AGP coding sequences present in the human genome. The larger majority of alpha AGP mRNA in human liver is transcribed from AGP‐A, whose promoter and cap site have been determined while the level of AGP‐B and B’ mRNA in human liver is very low. Using Hep3B hepatoma cells as a model system for the in vitro study of the acute phase reaction, we show that only AGP‐A is strongly induced by treatment with culture medium of LPS stimulated monocytes.