RECHARACTERIZATION OF THE START SITES FOR THE MAJOR HUMAN TRANSFORMING GROWTH-FACTOR-BETA-1 MESSENGER-RNA

The start sites for the major human TGF-beta 1 transcripts have been r eexamined. A comparison of ribonuclease and SI nuclease protection ana lyses on native TGF-beta 1 mRNA and in vitro transcribed human TGF-bet a 1 transcripts of defined sizes places the most 5' start site for the native TGF-beta 1 message approx. 50 nucleotides upstream from the pr eviously published start site at base +1. Furthermore, the same techni ques indicate that the apparent downstream start site at base +271 is an artefact due to the presence of an A + T-rich island in the middle of an otherwise highly G + C-rich sequence, This is not apparent if S1 nuclease protection is used alone, which emphasizes the importance of using the two techniques in combination for this type of analysis. Th us the major 2.5 kb TGF-beta 1 band seen on Northern blots comprises o nly mRNA transcribed from the more upstream of the two previously char acterized promoters. This has important implications both for the tran scriptional and translational regulation of this growth factor. (C) 19 97 Elsevier Science B.V.