The structure and sequence of the human c-sis/PDGF-2 growth factor have been determined by a combination of methods involving cDNA cloning, nuclease S1 mapping and primer extension. Nucleotide sequence analysis revealed that the 3373-nulceotide c-sis mRNA contained only 723-bp coding sequence for the PDGF-2 precursor polypeptide. The coding sequence was flanked by long 5' (1022-bp) and 3' (1625-bp) untranslated sequences. The entire gene is represented by seven exons, the majority of the first exon and entire seventh exon consisting of the noncoding sequences. The PDGF-2 gene promoter was localized 24 bp upstream of mRNA start site by nulceotide sequencing and chloramphenicol acetyl transferase (CAT) assays. By using CAT as a marker gene, we have localized negative regulatory sequences upstream as well as downstream of the prompter. Removal of the negative regulatory sequences resulted in the expression of PDGF-2 CAT sequences in fibroblasts which do not express the PDGF-2 transcript. Our studies indicate that strong secondary structures in the 5' noncoding region also regulate expression of the PDGF-2 polypeptide. Thus, we have determined the complete structure of the c-sis/PDGF-2 gene. Tissue-specific regulation of expression of this important growth factor is currently being investigated in detail.
