Purification and properties of a lambda operator-binding protein which is expected to be autorepressor (tof protein) from E. coli carrying lambdadv plasmid

In order to study the mode of action of the tof gene product, which is an "autorepressor" of the bacteriophage lambda and plasmid lambdadv, we have purified a DNA-binding protein which is specifically produced in bacteria carrying lambdadv. This protein possesses characteristics expected for the product of the tof gene, since it is produced under conditions where cI-repressor is not made, and since it binds to oL and oR operators on the lambda phage genome. The molecular weight of the native protein is 16,000-17,000 daltons, and the monomeric molecular weight as measured by gel electrophoresis in the presence of sodium dodecyl sulfate is about 10,000 daltons. Denaturation and renaturation experiments demonstrated that the native protein is a dimer of 10,000-dalton monomers. The lambdaDNA-specific binding protein is not produced in cells carrying i21dv or ø80dv.

Cloning bacterial genes with plasmid gammadv

recombinant molecules recovered from transformed E. coli cells consisted of a biologically functional bacterial DNA fragment and, excep

Role of the tof gene in the production and perpetuation of the lambdadv plasmid

A series of lambda derivatives carrying tof mutations were tested for their ability to give rise to plasmid lambda dv. Phages carrying tof mutations that distorted expression of the pRoR-tof-OP operon, were unable to produce lambda dv. Phages carrying an altered tof gene, having only a moderate effect on the same operon, produced unstable lambdadv's. On the other hand, those tof mutants were only the expression of the pLoL-N-exo operon, but not that of the pRoR-tof-OP operon was affected, produced stable lambdadv's.

Isolation and properties of a conditionally lethal bacteriophage lambda mutated in the chi region

A thermosensitive lambda phage mutant was isolated which can grow at high temperature only in the presence of the lambda chi gene product supplied in trans. This mutation tn was mapped within the chi region, and lambda tn phage expressed the pRoR-OP operon only poorly at high temperature. Effects of the tn mutation on expression of other operons were also examined and compared with those observed with cro27 or some tof mutations.

Mutants of Escherichia coli which block head formation of lambda

Five mutants of Escherichia coli K12 (lam 24, lam 25, lam 26, lam 27 and lam 646) that block head formation of lambda are described. In vitro complementation tests and electron microscopy demonstrated that in these bacteria phage tails were produced normally, whereas head formation was abnormal, aberrant head-related structures being produced. In lysates prepared from lam 24, lam 25 and lam 26, monsters and empty heads without tail were the predominant structures, whereas in lysates from lam 27 and lam 646, petit lambda and empty heads were the most common structures. The five lam mutations were located in two regions on the bacterial chromosome; lam 24, lam 25 and lam 26 were near the dnaB gene and lam 27 and lam 27 and lam 646 near the lac gene. It was suggested that the former three mutants are new isolates that belong to GroE mutants, whereas the latter two comprise a new group of mutants. Analyses of phage mutants (ov mutants) that overcome the interference by the lam 646 mutation revealed that this mutation blocks normal expression of the gene E of lambda.

Isolation and properties of Escherichia coli mutants which are nonpermissive for the growth of phage lambda

By selecting survivors of lambda phage infection, mutants of Escherichia coli K12 that block reproduction cycle of the phage have been isolated. Fourteen of these phage-tolerant mutants (lam mutants) were chosen and characterized biochemically and genetically. It was shown that these mutants were tolerant to infection by all the lambdoid phages, except for few cases, but they were susceptible to infection by a non-lambdoid temperate phage (phi299), P1 or T phages. The mutants can be divided into at least three groups: (1) A mutant (lam 16) strain that seems to block normal penetration of phage DNA: (2) Three mutant (lam 64, lam 67 and lam 71) strains that block an "early" step(s) of phage growth, including phage DNA synthesis: (3) Six mutant (lam 24, lam 25, lam 26, lam 27, lam 646 and lam 6) strains that block normal functioning of the gene E products and produce unusual head structures. Some lambdoid phages and lambda mutants that overcome the interference by the lam mutations have been obtained, and were used as tools for characterizing the host mutations. Two (lam 12 and lam 13) mutant strains and one (lam 1) mutant were inferred as affecting the expression of "late" genes, and early gene, respectively, by this test.

In vitro construction of different oligomeric forms of lambdadv DNA and studies of their transforming activities

Plasmid lambdadv1, which is in a dimeric form, was converted to a linear monomer duplex by the action of EcoRI restriction endonuclease that incises at a unique site in this plasmid genome. The resulting products were then joined by Escherichia coli DNA ligase to produce molecules with various oligomeric forms, and from these monomeric, dimeric, or trimeric circular molecules were purified. By transformation of cells with these DNAs, clones were obtained that carried lambdadv1 in a monomeric or dimeric form. The former type of clones have not been generated in vivo, except for one in a different host strain, and carriers of timeric or tetrameric lambdadv1's have not been obtained so far. It was observed that a considerable fraction of these oligomeric circular DNAs were converted to lower oligomers (e.g., from trimer to dimer) during transformation. The characteristics of the monomeric lambdadv1 carriers obtained were compared with those of dimeric lambdadv1 carriers. The stabilities of the plasmids of the two forms were the same. However, the monomeric plasmid carriers were less tolerant to lambdavir phage infection and perpetuated about 30% less plasmid genomes in monomer units. Furthermore, dimeric plasmid carriers appeared spontaneously and accumulated in cultures of the monomeric lambdadv1 carriers.

Intramitochondrial dense bodies in the goblet cells of the ileum of muscular dystrophic mice

Mitochondrial osmiophilic bodies were found in the goblet cells of the small intestine in a group of muscular dystrophic mice. They were not found in any littermate normal control mice. The dense bodies were uniformly round in shape but variable in size, approximately 0.2-0.4 mu in diameter. A limiting membrane encircled a dense content. Mitochondria with such dense bodies were distributed throughout the goblet cells. Adjacent absorbing epithelial cells had none of such mitochondrial bodies. Though the site of formation of the mitochondrial bodies remains to be investigated, the Golgi complex did not appear to be involved in the transportation of the dense bodies. Digestion of sections with ether-chlorofolm (1:1) slightly decreased the density of the mitochondrial body. Ruthenium red staining was not visible over the dense bodies but trace of Ru was detected by X-ray microanalysis. X-ray microanalysis indicated very few, if any, amounts of P and Ca, and it was not probable that phospholipid and calcium binding protein were the main constitution of these dense bodies.

Mode of replication of plasmid lambda-dv-1

About 20 copies of plasmid lambda-dv are perpetuated per host chromosome in Escherichia coli K12 cells. The mode of DNA replication of this plasmid lambda-dv was studied, using the density-labelling technique followed by banding in DsCl. It was shown that all the copies of plasmid lambda-dv are potentially capable of replicating roughly once a cell generation. Their replication occurs by random, that is a copy of the plasmid is taken out at random for replication from a pool, to which the two replicas resulting from replication are returned. Chloramphenicol did not inhibit the initiation of a new round of replication of the plasmid molecules, indicating that selection from the replication pool does not require concomitant protein synthesis.

Preparation of plasmid lambda dv from bacteriophage lambda: role of promoter-operator in the plasmid replicon

A technique has been described for selection of bacteria carrying plasmid lambdadv. With this technique, the effects of mutations in the promoter-operators were compared on the production and perpetuation of the plasmid. It was found that "left" promoter-operator that controls leftward gene expressions can be deleted from the plasmid genome. Some mutations of "right" promoter-operator (pRoR) that controls expression of genes tof, O, and P affect the stability of the plasmid. However, the plasmid genome accomodates a variety of pRoR mutations within a reasonable but different degree of constitutivity. Some new promoter mutations that allow bypass of the pRoR cannot be carried in the plasmid genome. From these findings it was proposed that the plasmid replicon has one indispensable promoter-operator that controls expression of all the genes related to its own replication, although a variety of constitutive mutations can be accommodated in the pRorR.

Interference in bacteriophage growth by a resident plasmid lambda dv. II. Role of the promoter-operator

The susceptibilities to interference by lambdadv of a set of lambda phages differing in the genetic structure of their right promoter-operator (pRoR) were compared. For this purpose mutant phages were added to lambdadv-carrier cells at various multiplicities, and abilities to escape from interference, as represented by percentages of infected complexes to produce progeny phages, were compared. It was observed that phages that carry strongly constitutive pRoR were able to escape from interference at a low multiplicity of infection, whereas phages with weakly constitutive pRoR were able to escape only when a large number of these genomes entered into a cell. Several mutations in the pRoR were arranged in order of their constitutivity, or ability to escape from interference. Next, the abilities of a set of lambdadv plasmids differing in their pRoR to cause interference were compared. The results showed that interference increased with increase in constitutivity of the pRoR in the plasmid genome. These observations are thought to reflect a regulatory system of the plasmid replicon, and a possible mechanism for the system is discussed.

Characterization of defective simian virus 40 DNA: comparison between large-plaque and small-plaque types

We characterized defective DNA molecules of large-plaque and small-plaque SV40 produced and accumulated during serial undiluted passages. The electron microscope heteroduplex method revealed that defective SV40 DNA contains deletions, insertions and substitutions. The majority of the large-plaque defective molecules had a simple deletion. The deletions were heterogeneous in size, and the sites of deletion appeared to be mostly overlapping. The majority of the small-plaque defective molecules had a deletion, and more than half of the deletion molecules also had an insertion at a separate site. The small-plaque SV40 genome appeared to have more sites for deletion to occur than large-plaque SV40, and the deletions have occurred at more than two sites. The change of a local nucleo tide sequence resulting from mutation may be related to the difference between the two plaque types.

Isolation of circular DNA molecules from whole cellular DNA by use of ATP-dependent deoxyribonuclease

A technique is described for isolation of plasmid DNA in closed and open circular double-stranded forms from bacterial cells, by use of ATP-dependent deoxyribonuclease purified from Micrococcus luteus. This DNase, acting only upon linear DNA molecules, degrades all bacterial chromosomal DNA extracted in the linear form. Circular plasmid DNAs are left intact, and are then separated by sedimentation through a sucrose gradient. Unlike previous techniques for analysis of plasmid DNA, this technique can be used to isolate not only closed circular DNA but also open circular DNA. Several plasmids, such as those from phage (lambdadv1 and lambdadv21), a colicinogenic factor (Col E2), a sex factor (F(8)' gal), and "minicircles" in Escherichia coli 15, in both the open and closed circular forms, were well separated from chromosomal DNA by this technique.