Establishment of an mRNA gradient depends on the promoter: an investigation of polarity in gene expression.
We found six mRNA species specific to the galactose operon of Escherichia coli. Analyses of both ends of the mRNAs indicated that while the 5' ends are fixed at the promoter region, the 3' ends vary along the operon. The resulting gal mRNA map suggests generation of an mRNA concentration gradient that is higher in the promoter-proximal region and lower toward the distal region. Real-time RT-PCR analyses of the amount of each mRNA species confirmed the existence of the gradient. This gradient of mRNA concentration could serve as an underlying mechanism for the long known phenomenon "natural polarity." Further analyses of the 3' ends of the mRNAs showed that they are generated by either an unknown mRNA processing/transcription termination mechanism(s) or Rho-dependent intra-cistronic transcription termination. The results showed also that transcription from the P2 promoter can yield a more severe mRNA gradient than that from the P1 promoter, suggesting that the slope of the mRNA gradient depends on which promoter the transcription has initiated from. These results led us to suggest a novel gene regulation model in which transcription initiation is tightly coupled to mRNA processing and/or transcription termination.
Lee
Hee Jung
HJ
Department of Biology, School of Biological Sciences and Biotechnology, Chungnam National University, Taejon 305-764, Republic of Korea.
Jeon
Heung Jin
HJ
Ji
Sang Chun
SC
Yun
Sang Hoon
SH
Lim
Heon M
HM
D000242:Cyclic AMP / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D005690:Galactose / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D009876:Operon / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism*; D024363:Transcription Initiation Site
D012333:RNA, Messenger; D000242:Cyclic AMP; D005690:Galactose