Isolation and characterization of Synechococcus PCC7942 promoters: tRNA(pro) gene functions as a promoter

Promoter-active fragments of Synechococcus PCC7942 were isolated by transcr iptional gene fusion to the promoterless beta-glucuronidase (GUS) gene of E . coli, which was used as a reporter gene. Several of the isolated promoter -active fragments expressed GUS activity in Synechococcus comparable to tha t of the lambda P-R promoter. Only 10% of the isolated promoter-active frag ments also functioned in E, coli. The transcription initiation sites of the two promoter-active fragments, D13 and E3, were identified. The major tran scription initiation sites of D13 and E3 in Synechococcus were located with in the nucleotides TTTG and TTG respectively, which were identical to those corresponding to E. coli. The inferred -10 and -35 regions of D13 were TAA ACT and TTGTAG respectively, which conformed to the E. coli sigma(70) promo ter. Immediately upstream of the E3 transcription initiation sites was the tRNA(pro) (GGG) gene, which contained two regions exhibiting strong homolog y to the major promoter elements in eukaryotic tRNA genes, but did not cont ain the E. coli promoter element. Thus, the tRNA(pro) gene can act as a pro moter.