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A Dual-Directed Control of Cell Wall Proteinase Production in Streptococcus cremoris AM₁: A Possible Mechanism of Regulation During Growth in Milk

Netherlands Institute for Dairy Research, Ede, The Netherlands

ABSTRACT

The production of cell wall proteinase in Streptococcus cremoris AM₁ can be effectively repressed at relatively low initial concentrations of an enzymatic digest of casein (containing mainly peptides) in the medium. In contrast, free amino acids did not affect proteinase production. In milk, production of proteinase proceeds uninterrupted but could be inhibited by the addition of peptides. The ability of cells to produce proteinase during the period of repression was demonstrated under conditions of complete inhibition of the transcription. The moment of appearance, the rate, and the duration of this transcriptional inhibitor-insensitive proteinase production is dependent upon the extent of metabolic consumption of external peptides. The occurrence of transcriptional inhibitor-insensitive proteinase production is likely to be indicative of derepression of proteinase-specific transcription and of inhibition of translation along newly synthesized proteinase-specific messenger ribonucleic acid (RNA). The view presented in this paper as a well-considered model for the regulation of cell wall proteinase production in S. cremoris AM₁ is compatible with the results and accounts for the observations in terms of preferential synthesis, involvement of a specific protein acting as a competitive messenger-specific represser, and accumulation of proteinase-specific messenger RNA. It provides in addition an adequate insight into the process of growth of this organism in milk.

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