CHARACTERIZATION OF A SALMON INSULIN-LIKE GROWTH-FACTOR-I PROMOTER

We have identified four transcription initiation sites in the salmon i nsulin-like growth factor I (IGF-I) gene. Use of the most upstream tra nscription start site generates a minor mRNA species with a 5' untrans lated region (UTR) of approximately 450-550 nucleotides, whereas trans cription starting at the downstream initiation sites results in more a bundant IGF-I mRNAs with 5'-UTRs approximately 250,245, and 165 nucleo tides in length. No consensus TATA box-like elements are present immed iately upstream of the most upstream start site identified, nor is thi s region particularly GC-rich. Transient expression assays, however, d emonstrated orientation-dependent promoter activity in a 386-nucleotid e-long fragment containing the major downstream transcription start si tes. Additionally, reverse transcriptase polymerase chain reaction (RT -PCR) analyses demonstrated tissue and developmental stage-specific us e of the various transcription start sites identified.