Truncated forms of Escherichia coli lactose permease: models for study of biosynthesis and membrane insertion.

Using in vitro DNA manipulations, we constructed different lacY alleles encoding mutant proteins of the Escherichia coli lactose carrier. With respect to structural models developed for lactose permease, the truncated polypeptides represent model systems containing approximately one, two, four, and five of the N-terminal membrane-spanning alpha-helices. In addition, a protein carrying a deletion of predicted helices 3 and 4 was obtained.

The upstream operator of the Escherichia coli galactose operon is sufficient for repression of transcription initiated at the cyclic AMP-stimulated promoter.

Two operators are known to bind Escherichia coli galactose repressor with roughly equal affinity. A study of the control these two operators exert on the two overlapping gal promoters is reported. The experiments rest on a set of mutations specifically constructed to inactivate individual control units of the gal operon and on quantitation of gal promoter activities.

Characterization of two mutations in the Escherichia coli galE gene inactivating the second galactose operator and comparative studies of repressor binding.

A series of plasmids has been constructed which contain either a single one of the two operators O1 and O2 of the Escherichia coli galactose operon or different combinations thereof. This permits comparison of the two operators with respect to their repressor binding ability. A plasmid containing only the second operator, O2, located within the structural gene galE, was found to titrate repressor in vivo and in vitro with essentially the same efficiency as a plasmid containing only the 'classical' galactose operator, O1, located upstream of the start of transcription.