REGULATION OF PTSH AND PTSL GENE-EXPRESSION IN STREPTOCOCCUS-SALIVARIUS ATCC-25975

The transcriptional regulation of the Streptococcus salivarius ptsH an d ptsl genes coding for the general energy-coupling proteins HPr and e nzyme I of the phosphoenolpyruvate:sugar phosphotransferase system wer e investigated. These genes form an operon with the gene order ptsH-pt sl. Three distinct mRNA species were detected: a 0.5 kb transcript spe cific for ptsH, and two long transcripts (2.2 and 2.4 kb) covering the whole pfs operon. Transcription of all these mRNAs initiated at the s ame nucleotide located 9 bp downstream from a promoter located immedia tely upstream from the ptsH gene. The presence of a high-energy stem-l oop structure (T-0) located at the begining of ptsl was responsible fo r the premature transcription termination generating the 0.5 kb ptsH-s pecific transcript. The long transcripts ended in the poly(U) region o f two rho-independent-like terminators (T-1 and T-2) at the 3' end of ptsl. Studies with a 2-deoxyglucose-resistant spontaneous mutant of S. salivarius (L26) that produces an HPr-El fusion protein suggest that the regulation of HPr and El expression involves transcriptional as we ll as translational mechanisms.