COMPARATIVE-ANALYSIS OF GENE-EXPRESSION IN STREPTOCOCCUS-PNEUMONIAE AND LACTOCOCCUS-LACTIS

The pFL10 plasmid vector for translational fusions was constructed. pF L10 is based in the promiscuous pLS1 replicon and contains the pC194 c at gene deprived of its transcriptional promoter and Shine-Dalgarno (S D) sequence. Three promoters P-cit, P-polA and P-tetL) from Gram-posit ive bacteria, inserted in pFL10, were tested for their ability to driv e transcription in Lactococcus lactis and Streptococcus pneumoniae. Th ese promoters were coupled to the SD sequence of the lactococcal citP gene fused to the cat gene. Determination of the 5' ends of the three mRNAs by primer extension revealed the same start sites in both bacter ial systems. However, it was observed a differential efficiency of pro moter utilization by the RNA polymerases from the two hosts. The trans criptional behavior correlates with expression of the cat gene measure d by determinations of chloramphenicol acetyltransferase (CAT) activit y. Substitution of the SD of citP by that of the T7 phi 10 gene render ed a similar decrease of the CAT production in both bacterial systems.