Regulation of pyrG gene expression in Lactococcus lactis is controlled by the amount of CTP through an attenuator mechanism involving reiterative transcription also known as stuttering
Special Symposium - Innovations in Food Technology (LMC Congress)
White BioTech & Related Processes (Food-2a)
Keywords: reiterative transcription, nucleotide metabolism, regulation of gene expression
Virtually all metabolic processes involve nucleotides - either directly as substrates or as allosteric effectors. Therefore, a constant supply of nucleotides is required for optimal growth. In order to fulfill this demand at all times during changing environmental conditions, the pathways leading to NTP are subject to regulation at both the genetic and the enzymatic level. In Lactococcus lactis - as in all organisms studied so far - CTP is formed de novo by an amination of UTP. The reaction is catalyzed by CTP synthase encoded by pyrG. The formation of CTP can be considered as a very simple pathway including only one reaction in which UTP is converted to CTP.
The objective of this project is to determine the impact of regulation at the genetic level in the adjustment of the CTP pool size. By using metabolic control analysis we were able to show, that the CTP synthase has full control of the CTP pool size; an increase in pyrG expression leads to an increase in CTP pool size, whereas the CTP pool size decreases during reduced pyrG expression. We have previously shown that pyrG expression is regulated by the CTP pool size. Therefore, the main conclusion is that the regulation of pyrG expression has the key role in CTP homeostasis at least in exponential growing cultures.
The regulation of pyrG expression is found to be regulated at the transcriptional level by attenuation. During high CTP levels a terminator structure immediately in front of the structural gene is preferentially formed, whereas low CTP levels leads to formation of an antiterminator. Evidence is presented that suggest that the intracellular CTP level is sensed by the speed of the RNA polymerase which determines whether additional G-residues are incorporated at the very start of the transcript.The number of G-residues determines which structure preferentially is formed. The addition of additional nucleotides in the start of a message is known as reiterative transcription or stuttering. In vitro data confirmed the model including the observation that no additional factor is required.
Presented Wednesday 19, 16:05 to 16:20, in session White BioTech & Related Processes (Food-2a).
