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The oxidation of isopropyl alcohol by chromic acid is a reaction first order with respect to the acid chromate ion, HCrO4−, first order with respect to the alcohol, and second order with respect to hydrogen ion. Evidence has been obtained that the reaction proceeds by way of a compound of tetravalent or of pentavalent chromium. On the basis of these facts, a mechanism for the oxidation has tentatively been suggested.

From physiological and genetic evidence, it is concluded that the repressor for β-galactosidase (EC 3.2.1.23) synthesis in a mutant bacterium, E-103, is thermolabile. The apparent inactivation of repressor is first order and irreversible; however, paradoxically, only a characteristic fraction can be inactivated at a given temperature, suggesting some heterogeneity of repressor in this strain. Following inactivation of repressor, there is a delay in reappearance of repression that is believed to be caused by the time required to establish synthesis of repressor.

Advantage is taken of the properties of a mutant in which the production of repressor for the Lac operon is temperature-sensitive to show that the formation of this repressor is not appreciably inducible by inducers (IPTG) under conditions in which the rate of β-galactosidase synthesis is increased one-thousandfold.

A procedure is described for the isolation of bacteria able to make unusually large quantities of β-galactosidase. A number of such hyper strains, as they are called, have been isolated and some have been found to make protein containing as much as 25% β-galactosidase. This enzyme in these strains appears to be identical with that in normal strains with respect to Michaelis constant, heat sensitivity, sedimentation constant, and ratio of antigenic sites to enzymic sites. The ability to make β-galactosidase at hyper rates is genetically determined in the lac region of the bacterial chromosome, and this ability can be transferred by genetic recombination.

The effects of ethanol on the growth of a wild-type Escherichia coli K-12 are described. These effects include a reduction of the steady-state growth rate and an interference with the division process. They appear as an immediate response to the addition of ethanol and are rapidly reversed by removal of ethanol. Mutants were selected that could grow at a concentration of ethanol that stopped wild-type growth. The growth of one of the mutants we studied (strain S9L100) is stimulated by the presence of ethanol, methanol, or dimethyl sulfoxide. This strain exhibits pleiotropic growth defects including abnormal cell division and morphology. It also appears to have an altered lac permease function which is not due to a mutation in the Y gene itself. We conclude that this mutant has an altered membrane and that the membrane defect may be the cause of the abnormal growth properties. The use of compounds which serve as general membrane perturbants and mutants resistant to these perturbants form a system accessible to both genetic and physical-biochemical techniques.

By experiments with mutants having temperature-sensitive repression systems for the Lac operon, it has been possible to provide evidence indicating that: (a) the i -gene product is the repressor, or physically included in it; (b) the rate of enzyme synthesis varies inversely with the first power of repressor concentration; (c) the repressor is “growth unstable” with a mean life of 1/5 to 1/10 generation; (d) inducers cause structural changes in repressor, manifested by altered thermal stability; (e) and the repressor is composed of subunits, which have a site for combination with inducers.

The nature of the repressors which control gene expression and the mechanism of their action promise to be clarified very soon largely because of the recent successful development of in vitro assays for the lac repressor (Gilbert and Muller-Hill, 1966) and for the repressor controlling the temperate phage λ (Ptashne, 1967). These developments have followed earlier experiments with whole cells which originally led to the postulation of repressors and which continued to provide further support for their existence. In the present report, I would like to describe some studies in whole cells of the interaction of galactoside inducers with the lac repressor.

Delbruck and Bailey (1) noticed an anomaly in the lysate of bacteria which was obtained by mixedly infecting the B strain of coli with the bacterial viruses T2 and T4. Subsequently, Luria (2) found this anomaly to be even more pronounced when he repeated Delbruck's experiment-using, however, virus T2 that had been exposed to ultraviolet irradiation. When we undertook experiments in an attempt to understand this anomaly, we were led to the following result: If we infect a culture of the B strain of coli mixedly with the bacterial viruses T2 and T4 and incubate to permit lysis of the bacteria, there are present in the lysate 3 easily distinguishable types of bacterial viruses. Two of these, as expected, behave like the original parent strains T2 and T4, i.e., one of them behaves like T2 inasmuch as it is unable to attack the mutant strain B/2 (which is resistant to T2) but is able to grow in the mutant strain B/4 (which is sensitive to T2); the other behaves like T4, being unable to attack B/4 (which is resistant to T4) but is able to grow in B/2 (which is sensitive to T4). The third type of virus present is phenotypically like T4 inasmuch as it is capable of multiplying in the strain B/2 (which is sensitive to T4), but it is genotypically like T2 inasmuch as, after one passage in the strain B/2, it is no longer capable of growing in it but is capable of growing in the strain B/4 (which is sensitive to T2). The presence of this third type of virus, which may be called "latent T2," can be demonstrated in the following manner: We add to a culture of the B strain of coli viruses T2 and T4 in ratios corresponding to 10 T2 and 10 T4 virus particles per bacterium, incubate to permit lysis of the bacteria, and then filter the lysate. If we plate a sample of this lysate on agar that is inoculated with the strain B/4 (which is sensitive to T2 but resistant to T4), those virus particles contained in the lysate which have the phenotype T2 will show up as plaques on these plates. T4 virus particles will not give plaques on this plate because B/4 is resistant to T4. The number of plaques is thus a measure of the number of T2 particles in the lysate. Using a sample of the lysate, we determine in this manner the number of plaques obtained on an agar plate inoculated with the strain B/4. When we repeat this experiment-with the difference that before plating on the B/4 plate we add to the sample of our lysate a certain quantity of the strain B/2, allow 5 min for absorption, dilute with broth, and incubate for 1 hr to permit lysis of the bacteria-then we obtain a ten to twenty-five times larger number of plaques on the B/4 plate. This phenomenon appears to show that there is present in our lysate a virus (the "latent T2") which is capable of multiplying in B/2 and subsequently forming plaques on B/4. In order to account for our observation, the concentration of the "latent T2" in the lysate would have to be about 10% of the concentration of T2. We were not able to obtain, after one passage in B/2, any appreciable further growth in B/2 of our hypothetical "latent T2." Before drawing the conclusion that the presence of a "latent T2" is in fact responsible for our phenomenon, it is necessary to exclude alternative explanations. As an alternative explanation of our observation, it appeared a priori conceivable that our lysate contains aggregates of virus particles formed by a T2 and a T4 particle that stick together. Such aggregates might then perhaps be capable of entering into a bacterium of the strain B/2 (by virtue of their T4 component) and, once inside, both virus particles T2 and T4 might then be able to multiply, and thus to produce the observed phenomenon. We were able to rule out this possibility, however, by performing the following experiment. We add to a sample of our lysate a certain quantity of B/2, using an excess of B/2 so that independent infection of one bacterium by more than one virus particle can be neglected. We then allow 5 min for absorption and plate on an agar plate that has been inoculated with both B/2 and B/4. If there are present any B/2 bacteria into which has entered an aggregate of virus particles composed of T2 and T4, and in which both viruses will grow, then a certain number of clear plaques centering around such bacteria (which yield both T2 and T4) should develop on the agar plate. We were not able to find any such clear plaques, however, and found only turbid plaques (in which either the B/2 is lysed by T4 or the B/4 is lysed by T2). This rules out the alternative explanation of our phenomenon. We ascertained that our phenomenon is produced under conditions in which we use an excess of B/2, so that independent infection of one bacterium by more than one virus particle can be neglected. We also ascertained that our phenomenon is not produced if, in place of our lysate, we use a mixture of T2 and T4. We are thus led to conclude that the phenomenon described is due to virus particles that have the phe