REGULATION OF ILVA EXPRESSION (NON-COORDINATE, OVERLAPPING)
Abstract
The control of ilvA expression in a variety of plasmid vectors has been studied to elucidate the means by which ilvA is normally expressed at a lower level than are the genes preceding it in the ilvGMEDA operon but is expressed at a much higher level when the isoleucine supply is limited. The DNA sequence of the gene has been obtained and analyzed to examine the possibility that the DNA may contain signals resulting in the non-coordinate expression of the operon and the downstream amplification of ilvA. A DNA fragment containing the entire ilvA gene and short flanking regions encoding the 3' ends of the ilvD and ilvY genes has been inserted into the pUC plasmids such that the ilv insert is in the six possible reading frames relative to the lacZ promoter and ribosome binding site of the vector. Only one of the six plasmids expresses ilvA. DNA sequence analyses indicate that a ribosome initiating translation at the lacZ in pEH31 would translate the ilvD portion of the insert in the wrong reading frame, stopping prematurely at a TAA signal that overlaps a rare AUA isoleucine codon in the ilvD reading frame. The translational coupling of ilvD and ilvA in this plasmid may mimic the normal coupling when isoleucine is in short supply. A variety of lacZ'-ilv'DA'-lac'Z' plasmids have been constructed to study the effect of the location of translation termination of ilvD on expression of ilvA. A model for ilvA expression is proposed.
Degree
Ph.D.
Subject Area
Molecular biology
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.