Fine tuning of Des transcriptional regulation

NAJLE, SEBASTIÁN R.; INDA, MARÍA EUGENIA; DE MENDOZA, DIEGO; CYBULSKI, LARISA E.

Carlos Paz, Córdoba, Argentina

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Bioquímica y Biología Molecular (SAIB).; 2008

Membrane fluidity is tightly regulated by the Des system in Bacillus subtilis. This system  is composed of a membrane histidine kinase, DesK, that phosphorylates the response regulator, DesR, when the membrane becomes rigid. Only the phosphorylated form of DesR activates the transcription of the D5-acyl-lipid desaturase gene. In this study we have examined the role of the N-terminal domain of DesR, that contains the phosphrylatable conserved residue Asp 54 by constructing a truncated DesR protein, lacking the first 128 amino acids, C-DesR. Our data demonstrate that C-DesR is able to bind to the des promoter in EMSA, but unable to stimulate transcription in vivo. We propose that the mechanism by which DesR is activated by phosphorylation implies release of the inhibitory effects of the N-terminal regulatory domain over the C-terminal domain containing the HTH motif. Besides, the effect of deletion of 0.5;1 or 1.5 DNA–helix  turn of the low affinity site of the des promoter was evaluated by EMSA and transcriptional fusions. From this study we can conclude that a dimer of phosphorylated DesR bound to the high affinity site element in phase and close enough to the -35 is sufficient to activate des transcription, suggesting that the low affinity site functions as a threshold barrier for basal expression.