AN EXTENDED -10-PROMOTER ALONE DIRECTS TRANSCRIPTION OF THE DPNII OPERON OF STREPTOCOCCUS-PNEUMONIAE

The genetic cassette encoding the DpnII restriction-modification syste m of Streptococcus pneumoniae gave transcription products of approxima tely 2.7 and 1.8 kilobases. The larger, mRNA1, covered bath of the met hylase genes, dpnM and dpnA, and the endonuclease gene dpnB; the small er, mRNA2, covered only the dpnA and dpnB genes. Transcription of mRNA 1 was shown to begin at the translation start site for dpnM, thereby p roducing an mRNA without any apparent ribosome-binding site for transl ation of the DpnM methylase. The promoter far 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 u pstream with close matches to a -35 site and a nonextended -10 site wa s not used. A survey of 36 proven and putative promoters used by S. pn eumoniae revealed that 61% of them contained the full -10 extension, a lthough, other than the dpnM promoter, they matched at a -35 site, as well. It appears that, unlike those found in Escherichia coli, S. pneu moniae promoters frequently require an extended -10 site, and such a s ite can function naturally without a -35 site.