PROLINE BIOSYNTHESIS IN STREPTOCOCCUS-THERMOPHILUS - CHARACTERIZATIONOF THE PROBA OPERON AND ITS PRODUCTS

The presence of proline in the medium was not essential for growth of Streptococcus thermophilus, indicating that there is a proline biosynt hetic pathway in this organism. Genetic and biochemical analysis ident ified and characterized this pathway. Two genes, designated proB and p roA, were cloned, sequenced and characterized. Biochemical analysis of the proB- and proA-encoded enzymes showed that the proline biosynthet ic pathway of S. thermophilus is similar to the one previously describ ed in Escherichia coli. The deduced amino acid sequence of a 2.408 kb DNA region containing the genes revealed the similarity of the S. ther mophilus gene products to ProB and ProA of E. coli and Serratia marces cens, and to the corresponding N- and C-terminal domains of the bifunc tional plant enzyme Delta(1)-pyrroline-5-carboxylate synthetase of Vig na aconitifolia. Northern blot analysis showed that the two genes in S . thermophilus are organized in a single operon with proB proximal and proA distal to the promoter; primer extension analysis indicated that proBA transcription is not under repressive control by exogenously su pplied proline.