PHYSIOLOGICAL AND GENETIC-REGULATION OF RIBOSOMAL-RNA SYNTHESIS IN LACTOCOCCUS

The macromolecular composition of Lactococcus was regulated by growth rate in the same general way as that of less fastidious bacteria such as Escherichia coli and Salmonella typhimurium. The ratios of RNA:DNA and RNA:protein increased approximately threefold over a 13.5-fold inc rease in growth rate, whereas the ratio of DNA:protein remained approx imately constant. Using reporter genes fused to a DNA fragment of a cl oned lactococcal rRNA operon, promoter activity was located upstream o f the 16S rRNA structural gene. This DNA fragment had some characteris tics typical of a rrn promoter in E. coli. Two consensus promoter sequ ences P1 and P2 were located 296 and 157 bp, respectively, upstream of the start of the 16S rRNA gene. Between P2 and the start of the 16S r RNA gene, sequences were identified with typical anti-termination moti fs characteristic of E. coli rrn promoter regions. A putative transcri ption terminator sequence was identified downstream of the 5S rRNA gen e and putative primary RNA transcript processing sites at both ends of the lactococcal rRNA operon were also noted.