Induction and transcription studies of the dextransucrase gene in Leuconostoc mesenteroides NRRL B-512F

Dextransucrase production by Lenconostoc mesenteroides NRRL B-512F in media containing carbon sources other than sucrose is reported for the first tim e. Dextransucrases were analyzed by gel electrophoresis and by an in situ a ctivity assay. Their polymers and acceptor reaction products were also comp ared by C-13 nuclear magnetic resonance and high-performance liquid chromat ography techniques, respectively. From these analyses, it was found that, i ndependently of the carbon source, L. mesenteroides NRRL B-512F produced de xtransucrases of the same size and product specificity. The 5' ends of dext ransucrase mRNAs isolated from cells grown under different culture conditio ns were identical. Based on this evidence, we conclude that dextransucrases obtained from cells grown on the various carbon sources result from the tr anscription of the same gene. The control of expression occurs at this leve l. The low dextransucrase yields from cultures in D-glucose or D-fructose a nd the enhancement of dextransucrase gene transcription in the presence of sucrose suggest that an activating phenomenon may be involved in the expres sion mechanism. Dextransucrase mRNA has a size of approximately 4.8 kb, ind icating that the gene is located in a monocistronic operon, The transcripti on start point was localized 34 bp upstream from the ATG start codon, The - 10 and -35 sequences found, TATAAT and TTTACA, were highly homologous to th e only glycosyltransferase promoter sequence reported for lactic acid bacte ria.