Fatty Acid Degradation in <i>Escherichia coli</i> : Requirement of Cyclic Adenosine Monophosphate and Cyclic Adenosine Monophosphate Receptor Protein for Enzyme Synthesis

The strong repression of inducible synthesis of the enzymes of fatty acid degradation by glucose can be partially relieved by the addition of cyclic adenosine 3′,5′ monophosphate (cyclic AMP) to the growth medium. This reversal of the glucose effect by cyclic AMP is not observed in a mutant (K29) that is unable to grow on fatty acids as sole carbon source and that was found to synthesize low levels of several enzymes specified by the fad regulon. In a revertant selected for the ability to grow on oleate these effects are concomitantly relieved. By both genetic (co-transduction of the mutation with the strA locus) and biochemical experiments (an extract of the mutant strain does not show the cyclic AMP-dependent stimulation of the deoxyribonucleic acid-directed in vitro synthesis of the enzymes of the gal operon), it is demonstrated that the mutant lacks functional cyclic AMP receptor protein (CR protein). It is concluded that, like many other inducible enzyme systems, expression of the enzymes of the fad system requires cyclic AMP and the CR protein. </jats:p

Construction and in vivo analysis of new split lactose permeases

AbstractThe capacity of incomplete segments of Escherichia coli lactose permease to form transport-competent complexes in vivo was further tested. Two series of mutant lacY genes were constructed. One encoded N-terminal lactose permease segments of different length. The proteins specified by the other group contained deletions of different length and location within the N-terminal region. Several pairs of such mutant proteins reconstituted active lactose transport. For certain combinations duplications of protein segments were compatible with the formation of an active carrier. Duplication of helices could also be tolerated, when part of a single polypeptide chain

Topological analysis of the amino-terminal region of lactose permease using the Escherichia coli outer membrane protein, OmpA, as a marker

AbstractLacY-ompA fusions, encoding the N-terminal 50, 71 or 143 residues of lactose permease, were constructed. The observed orientation of the OmpA part of each hybrid protein with respect to the plasma membrane supports current models of the N-terminus of Lac permease. Hybrids possessing the entire mature OmpA were very stable; those with only a part thereof were much less stable. Due to their in vivo stability and accessibility to antibody it is proposed that such hybrids may represent potential models to investigate the assembly pathway of lactose permease