GALECTIN-3 - DIFFERENTIAL ACCUMULATION OF DISTINCT MESSENGER-RNAS IN SERUM-STIMULATED MOUSE 3T3 FIBROBLASTS

The murine Galectin-3 gene spans similar to 12 kb of DNA and contains six exons, with the translation initiation codon located in exon II. O n the basis of restriction mapping and sequence analysis of the DNA up stream of exon II, primer extension assays, rapid amplification of cDN A ends, and ribonuclease protection assays were designed and carried o ut to determine the initiation site of transcription and the sequence of exon I. The results revealed at least two transcription initiation sites (alpha and delta), each of which appears to be specifically asso ciated with the use of alternative donor splice sites, resulting in di stinct mRNA species. Type I message initiates at transcription start s ite delta, uses splice donor site No. 2, retaining a 27 bp sequence, w hereas type II message initiates at transcription start site alpha, us es splice donor site No, 1, resulting in the loss of the 27 bp sequenc e. Primer extension assays carried out with mRNA isolated from 3T3 fib roblasts at various times after serum stimulation indicate that while the type II message varies in level only a little over the first 20 h, there is dramatic accumulation of the type I message, which peaks at 16h post mitogen addition.