Promoter activity of the two chicken delta-crystallin genes in a Hela cell extract

The in vitro transcriptional activity of the two delta-crystallin genes (5'-delta 1-delta 2-3') of the chicken was studied in a whole Hela cell extract. Both the delta 1 and delta 2 promoters were recognized by RNA polymerase II in this heterologous system. The major RNA initiation site from the delta 1 promoter was the same in vitro as that which occurs in vivo, as judged by mapping with S1-nuclease, although other minor initiation sites upstream and downstream of the major initiation site were noted. A primer extension experiment showed that the longest RNA synthesized in vitro from a delta 2 template initiated near the beginning of the first exon. The delta 1 promoter was several-fold stronger than that of delta 2 under the present in vitro conditions. Transcription from the delta 1 promoter was abolished by a competitor fragment (c'-II; includes -328 to -63) purified from the delta 2 promoter, indicating that one or more common transcription factors binding upstream from the TATA box are required for in vitro function of the two delta-crystallin promoters. Thus, in the Hela cell extract both delta-crystallin genes contain a functional promoter. We consider the possibility that the single 5'CCAAT3' sequence present in the delta 1 promoter (but lacking in the delta 2 promoter) may contribute to its greater core activity under our conditions. The greater promoter activity of the delta 1-crystallin gene in the Hela cell extract was not sufficient to account for the large ratio of delta 1 to delta 2 mRNA (approximately 50 to 100) in the embryonic chicken lens.