Arthur Weissbach

Thymineless induction in Escherichia coli K12(λ)

Abstract 1. 1. Thymine deprivation of a thymineless auxotroph of Escherichia coli K12(λ) leads to the induction of λ. This phenomenon does not result from carbon, nitrogen or phosphorus starvation. 2. 2. Conditions which prevent thymineless death also inhibit thymineless induction. However, the two phenomena may not be necessarily interdependent. 3. 3. In low phosphate-containing media, adapted cells of K12(λ)-thy − do not lyse, when induced by thymine deprivation or with mitomycin C. However, lysis occurs almost immediately upon the addition of phosphate to the induced cells.

Formation of intermediates in the replication of phage lambda DNA

After induction of Escherichia coli K12(λ) by ultraviolet light, a large part of the newly synthesized DNA is present as intermediate forms which are clearly distinguishable from mature λ DNA. One of the new DNA species is very sensitive to shearing and shows a relatively high sedimentation rate when compared to normal λ DNA. Its properties are consistent with those of a long, linear, concatenated structure. The intermediate forms of λ DNA are apparently formed from smaller DNA molecules the size of mature λ DNA. In the latter part of the latent period just before cell lysis, these large intermediates are broken down to DNA of the size found in the normal phage particle. λsusA and λsusD mutants have been found to accumulate large amounts of the intermediate during λ DNA synthesis and are unable to convert them to mature phage DNA.

The enzymic determination of myo-inositol

An inositol dehydrogenase obtained from myo-inositol-grown Aerobacter aerogenes has been adapted for the determination of myo-inositol in microgram amounts. The other cyclitols and sugars tested do not interfere with this assay, though colchicine exerts a marked inhibitory effect.

A study of the deoxyribonucleases and deoxyribonucleic acid polymerase of Escherichia coli K12S after infection with the bacteriopahge T4r

Abstract T4r infection of Escherichia coli K12S leads to a 4-fold rise in both DNAase and DNA polymerase (deoxynucleoside triphosphate: DNA deoxynucleotidyltransferase, EC 2.7.7.7) activities after 10 min. Part of the increase in nuclease activity seems to be due to the formation of an exonuclease chromatographically associated with DNA polymerase. The new exonuclease associated with λ phage formation in K12S is not seen after T4r infection of K12S. A large part of the DNA polymerase activity in normal or T4r-infected cells is attached to ribosomes when extracts are prepared in the presence of 0.01 M Mg2+. In normal cells the polymerase activity is released from the ribosomes in the absence of Mg2+. In contrast, in T4r-infected cells, ribosomal particles prepared in the absence of Mg2+ still contain significant amounts of DNA polymerase activity.

A novel system for the incorporation of amino acids by extracts of E. coli B.

The incorporation of leucine into an acid insoluble product has been observed in an in vitro system obtained from E. coli. This system contains a particulate fraction, a soluble fraction and RNA. Only certain amino acids are fixed by this system, which is not inhibited by chloramphenicol or lecithinase A. n nOptimal incorporation requires ATP, Mg++, inorganic phosphate, and a sulfhydryl containing compound, and shows characteristics previously undescribed for the incorporation of amino acids.

The appearance of circular DNA after lysogenic induction in Escherichia coli CR34(λ)

A circular (non-ended) form of DNA is synthesized both after ultraviolet light and after thymineless induction of the lysogen Escherichia coli CR34(lambda). This new DNA species is shown to have characteristics identical to the circular DNA formed from lambda phage DNA immediatelyafter infection. Thus, the formation of a circular lambda DNA isnot limited to that derived directly from an infecting phage DNA but is also formed during the normal replication of the lambda DNA after lysogenic induction. The circular lambda DNA formed after lysogenic induction contains no detectable amounts of the bacterial genome. Once formed in the cell, the circular DNA species is stable and not significantly degraded.

Studies on the formation of circular λ DNA

Abstract A circular form of λ DNA is synthesized within 5 minutes after phage infection of sensitive and lysogenic cells of Escherichia coli K12 at phage multiplicities of 5 and 0.8 phage per bacterium. The amount of circular λ DNA formed in infected lysogenic cells is 2 to 3 times that found in sensitive cells infected under comparable conditions. The circular DNA species is also synthesized when λ phage superinfects lysogenic cells which had previously been induced by ultraviolet light or thymine deprivation. Although the mechanism for synthesis of the circular λ DNA species is not known, evidence is presented that it does not involve the incorporation of thymine or inorganic phosphate.

The degradation of twisted circular lambda DNA by phage lambda mutants

The stability of the twisted circular, covalent form of phage lambda DNA (species I) has been examined after infection of thymine auxotrophs of E. coli with early sus mutants and integration negative mutants of lambda. After infection of the permissive host, E. coli CR34 (thy−), all of the lambda mutants tested lost over 90% of their species I DNA after 60 minutes of incubation in a thymine deficient medium. In the nonpermissive host, E. coli W3350 (thy−), it was found that the sus P lambda mutants were the least efficient in degrading species I phage DNA. It is suggested that the P cistron may be involved in directing the synthesis of a phage specific endonuclease which attacks the twisted, circular, covalent configuration of phage DNA.