Human p150,95 alpha-subunit: genomic organization and analysis of the 5'-flanking region

LFA-1, Mac-1, and p150,95 comprise a family of cell-surface glycoproteins that mediate adhesive interactions of myeloid and lymphoid cells. These glycoproteins are heterodimers composed of a common beta-subunit and distinct alpha-subunits. The chromosomal gene for the alpha-subunit of p150,95 was isolated to provide a framework from which to study the mechanisms for expression of the gene. The gene spans 30 kb of DNA and contains 31 exons. In agreement with a previous report by Corbi et al. (1990), the exons were found to be divided into five groups separated by large introns. The extracellular domains are encoded in exons 2 through 30 while the transmembrane and cytoplasmic domains are encoded in exons 30 and 31. We have expanded these findings in a number of ways. The first exon contains the 5' untranslated region. The 2,163-bp 5'-flanking sequence contains the first intron and several putative transcriptional initiation sites preceded by two TATA sequences and two GC-like boxes. Additional sequence motifs for a variety of DNA-binding proteins are present and discussed. Fusions of the bacterial chloramphenicol acetyltransferase gene (CAT) to approximately 5.3 kb of 5'-flanking DNA and also to subcloned fragments of this region were constructed and transfected into the human promonocytic cell line, U937. CAT expression was inducible with phorbol-12-myristate-13-acetate (PMA) and full expression was dependent on the presence of intron 1 and sequences upstream from the 2,163-bp flanking DNA. Additionally, intron 1 and a region further upstream contain functional cis-acting sequences.