STRUCTURE OF THE MURINE MAC-2 GENE - SPLICE VARIANTS ENCODE PROTEINS LACKING FUNCTIONAL SIGNAL PEPTIDES

The murine Mac-2 gene is composed of six exons dispersed over 10.5 kil obases. Sl nuclease mapping showed multiple transcription initiation s ites, clustered within a 30-base pair region. Sequence analysis reveal ed that a consensus initiator sequence is located in this area which l acks a TATA motif. The untranslated first exon contains an alternative splice donor site, confirming the existence of two cDNA species with the potential to encode proteins differing at their NH2 termini. In vi tro expression and translocation experiments demonstrate that both of the alternatively spliced variants of Mac-2 encode proteins which lack a functional signal peptide. Subcellular fractionation studies indica te that most of the Mac-2 protein is present in the cytosol. These res ults support the view that Mac-2 is exported from the cell by an unusu al mechanism which does not depend on the presence of a signal peptide .