Chapter 15, Problem 16PDQ

A marine bacterium is isolated and is shown to contain an inducible operon whose genetic products metabolize oil when it is encountered in the environment. Investigation demonstrates that the operon is under positive control and that there is a reg gene whose product interacts with an operator region (o) to regulate the structural genes designated sg.

In an attempt to understand how the operon functions, a constitutive mutant strain and several partial diploid strains were isolated and tested with the results shown here:

Host Chromosome	F' Factor	Phenotype
wild type	none	inducible
wild type	reg gene from mutant strain	inducible
wild type	operon from mutant strain	constitutive
mutant strain	reg gene from wild type	constitutive

Draw all possible conclusions about the mutation as well as the nature of regulation of the operon. Is the constitutive mutation in the trans-acting reg element or in the cis-acting o operator element?