An Extended −10 Promoter Alone Directs Transcription of the DpnII Operon of Streptococcus pneumoniae

The genetic cassette encoding the DpnII restriction–modification system of Streptococcus pneumoniaegave transcription products of approximately 2.7 and 1.8 kilobases. The larger, mRNA1, covered both of the methylase genes, dpnMand dpnA, and the endonuclease gene dpnB; the smaller, mRNA2, covered only the dpnAand dpnBgenes. Transcription of mRNA1 was shown to begin at the translation start site for dpnM, thereby producing an mRNA without any apparent ribosome-binding site for translation of the DpnM methylase. The promoter for mRNA1 was shown by base substitution and deletion analysis to consist of an extended −10 site TaTGgTATAAT, with no required −35 site. A possible promoter further upstream with close matches to a −35 site and a nonextended −10 site was not used. A survey of 36 proven and putative promoters used by S. pueumoniaerevealed that 61% of them contained the full −10 extension, although, other than the dpnMpromoter, they matched at a −35 site, as well. It appears that, unlike those found in Escherichia coli, S. pneumoniaepromoters frequently require and extended −10 site, and such a site can function naturally without a −35 site. f2 f2 Abbreviations used: ARBS, atypical ribosome-binding site; Cm r, chloramphenicol resistance.