NEW CONTROL MECHANISMS INVOLVED IN THE REGULATION OF THE THR, ILV, AND LEU OPERONS OF ESCHERICHIA COLI K-12
Abstract
Mutants of Escherichia coli K-12 resistant either to the threonine analog, DL-(alpha)-amino-(beta)-hydroxyvaleric acid (AVA), or to the leucine analog, 5,5,5-trifluoro-DL-leucine (FL), were isolated. One AVA resistant mutant strain, designated SP572, constitutively expressed the thr and ilv operons. The mutant allele, avr-16, was localized between trpR and the thr operon at minute 0. The wild-type allele of avr-16, designated ileR, is trans dominant. One FL resistant mutant strain, designated FLR9, expressed the leu and ilv operons constitutively. The mutant allele, flr-9, is linked to entA at minute 13. The wild-type allele of flr-9, is designated leuJ. The constitutive expression of the thr, ilv, and leu operons in mutants avr-16 and flr-9 was partly reversed in cells harboring a plasmid which leads to elevated levels of the trpR gene product, the Trp aporepressor protein. I have cloned ileR('+) as a 9.5 Kb EcoRI-SalI fragment into the multicopy plasmid pBR322. Subcloning experiments have localized ileR('+) to a 1.2 Kb BglII-SalI fragment. When ileR mutations were introduced into strains harboring attenuation-defective fusions of lacZ to the promoter regions of the thr and ilv operons, further depression of (beta)-galactosidase above that of the de-attenuated levels was observed. Cells harboring either plasmids containing ileR('+) or plasmids leading to the hyperproduction of Trp repressor displayed repression of both operons. Utilizing deletion mutants, I have identified two additional positive regulatory elements that act to control the thr and ilv operons. My results support the idea that ileR('+) encodes a true repressor protein which negatively controls the expression of the thr and ilv operons and that positive as well as negative controlling elements act independently of attenuation to further modulate these systems.
Degree
Ph.D.
Subject Area
Genetics
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