SYNTHESIS OF BETA-D-GALACTOSIDASE AFTER F-DUCTION OF LAC+GENES INTO ESCHERICHIA COLI

Nucleotide sequence at the end of the gene for the RNA polymerase beta' subunit (rpoC)

We have determined the DNA sequence surrounding the transcription terminator following rpoC, the gene that codes for the beta' subunit of RNA polymerase in E. coli K12. The 2044 bp sequence obtained contains the distal 335 codons of rpoC followed by a 212 bp non-coding region and a second open reading frame (ORFa) of 179 codons. The final 181 nucleotides of the sequence form the 5' end of a third open reading frame (ORFb). The in vivo 3' end of the rpoC mRNA was located by analysis of RNA/DNA hybrids cleaved with nuclease S1 (S1 mapping). These results indicated that the major transcription termination of the rplJL-rpoBC transcription unit occurs a short distance past the translation stop codon for rpoC. Four regions of symmetry, suggesting secondary structure in the mRNA, were found in the DNA sequence near the rpoC translation termination codon. The last of these hairpin structures is similar to other rho-independent transcription terminators and its 3' end coincides with the end of the rpoC mRNA as predicted by S1-mapping. Inspection of the open reading frames indicates that rpoC uses a high percentage of codons that are recognized by the major tRNA species of E. coli while ORFa and ORFb contain many codons recognized by minor tRNA species. ORFa specifies a very basic peptide.

Repression of diaminopimelic acid decarboxylase in Escherichia coli: gene dosage effects and escape synthesis

Gene dosage and escape synthesis experiments support the hypothesis that diaminopimelate decarboxylase repression by lysine involves a repressor molecule in a negative control system.

The regulatory nature of the phoB gene for alkaline phosphatase synthesis in Escherichia coli

Quantitative measurements of alkaline phosphatase activity in various merozygotic combinations and electrophoretic analyses of periplasmic proteins derepressed by phosphate-starvation show that phoB is a positive regulatory gene.

Conjugation in Escherichia coli: a study of recombination and the fate of donor DNA at the level of the zygote

We have developed an experimental system for studying concomitantly the fate of the donor DNA and the process of recombination after conjugation in Escherichia coli. We used a set of Hfr and F-strains carrying complementing lacZ mutations. Expression of the lacZ allele on the chromosomal fragment derived from the donor results in the formation of heat sensitive beta-galactosidase by complementation. By intragenic recombination between the two lacZ mutations a lacZ+ gene may be formed, and wild type beta-galactosidase will be synthesized subsequently. So the assay of heat sensitive and wild type beta-galactosidase enabled us to follow respectively the fate of the donor DNA and the recombination process. Using various recombination deficient recipient strains, we found that the donor DNA is progressively inactivated in recA, rec-34 and recH recipients, although the initial rate of expression is equivalent to that in a Rec+ recipient; no significant recombination was observed. In Rec+, recB or recG recipients there was no inactivation and recombination occurred. The kinetics of recombinant formation in the recB strain seems to differ from the wild type; in a recG recipient the recombination activity is significant, but lower than in the wild type recipient.

Mapping loci for surface exclusion and incompatibility on the F factor of Escherichia coli K-12

A series of Hfr deletion strains carrying deletions extending different distances into the integrated F factor have been used to map loci for surface exclusion (traS) and for incompatibility (inc) on the Escherichia coli K-12 sex factor F. traS mapped between traG and traD. It forms a part of the large operon, including all the known transfer genes except traJ, and is co-controlled with these. The product of traS is not required for formation of the F pilus. inc mapped between the phi(R) (11) locus and the origin of transfer; it is therefore one of the earliest loci transferred during conjugation.

Plasmid-associated functions of a stable Flac

Several functions associated with the stable plasmid, FlacS, have been examined. Our results indicate that the sex pili synthesized by Escherichia coli strains carrying FlacS are altered in some manner as evidenced by a very inefficient adsorption of male-specific phages. On the other hand, FlacS-mediated entry exclusion of related plasmids and plasmid incompatibility function(s) appear normal. The presence of covalently closed circular deoxyribonucleic acid in E. coli strains harboring FlacS indicates that it is an autonomously replicating plasmid. Based on beta-galactosidase levels and the percentage of covalently closed circular deoxyribonucleic acid, it appears that the stability of the FlacS is not the result of multiple copies of this plasmid. FlacS appears larger than its precursor, F(ts114)lac, in sedimentation through alkaline sucrose gradients.

Genetic and physicochemical characterization of Escherichia coli strains carrying fused F' elements derived from KLF1 and F57

Although the two F' elements, F57 (carrying his(+)) and KLF1 (carrying leu(+)), cannot normally coexist in the same cell, crosses between RecA(-) strains of Escherichia coli carrying these two elements gave rise, at a low frequency, to progeny carrying both the his(+) and leu(+) markers in an extrachromosomal state. Genetic studies showed that the his(+) and leu(+) markers were now linked, and centrifugation studies of F' DNA isolated from these strains confirmed the presence of a new species of DNA molecule of altered size. It is proposed that the his(+) and leu(+) genes in these strains are covalently linked on a single "fused" F' element.

Studies on Escherichia coli sex factors: evidence that covalent circles exist within cells and the general problem of isolation of covalent circles

We examined in detail conditions necessary for making reproducible and for maximizing the amount of deoxyribonucleic acid obtained from a sex factor-containing cell as covalent circles. The results argue that under optimal conditions covalent circles are neither created nor lost during the isolation procedure. The causes of the culture-to-culture variation in recovery of covalent circular deoxyribonucleic acid were investigated but an understanding of this is not yet at hand. Some commonly used conditions which drastically reduce the recovery of covalent circles are described.

Wild-type strain of Staphylococcus aureus containing two genetic linkage groups for penicillinase production

Staphylococcus aureus strain 55C1, isolated from a patient in 1955, contained two genetic linkage groups for penicillinase formation. One was linked to genes that control resistance to cadmium and mercuric ions; it had properties of a plasmidborne gene. The other was not linked to resistance to these metal ions; it had properties of a chromosomal gene. Penicillinase formation by cells that contained either linkage group was inducible by penicillins. Induced penicillinase in cells that contained both linkage groups equalled the sum of that produced in cells containing each group singly. Exopenicillinase produced by cells containing either gene was serological type A. Constitutive penicillinase formation resulting from regulator gene mutations in either linkage group was repressed to differing extents by a wild-type determinant in the trans position. The genetic structure and the regulation of penicillinase formation in strain 55C1 resembled in general those for penicillinase linkage groups which Asheshov and Dyke described for diploid mutant strains of S. aureus PS 80. There were differences in detail, however.

Inhibition of replication of an F'lac episome in Hfr cells of Escherichia coli

Hfr strains of Escherichia coli K-12 were found capable of accepting a F'lac episome during mating, with a frequency approximating that of F(-) strains. However, the F'lac episome was unable to replicate in the Hfr cells, and was diluted out during the growth of the culture. The lac(+) gene of the episome can be "rescued" by recombination into the host chromosome, as shown by the appearance of variegated recombinant colonies on a lactose-fermentation indicator medium. In recA Hfr strains, however, no lac(+) offspring were obtained in crosses with F'lac donors. The induced synthesis of beta-galactosidase in F'lac(+) x Hfr zygotes was studied. Rates of enzyme synthesis were approximately constant with respect to time as expected from unilinear inheritance of the F'lac episome. However, the rate of synthesis eventually increased, presumably due to integration of the lac(+) gene in some of the zygotes. In F'lac(+) x recA Hfr zygotes the rate of beta-galactosidase synthesis remained constant with respect to time, as expected.

Transient repression of the lac operon

Severe transient repression of constitutive or induced beta-galactosidase synthesis occurs upon the addition of glucose to cells of Escherichia coli growing on glycerol, succinic acid, or lactic acid. Only mutants particularily well adapted to growth on glucose exhibit this phenomenon when transferred to a glucose-containing medium. No change in ribonucleic acid (RNA) metabolism was observed during transient repression. We could show that transient repression is pleiotropic, affecting all products of the lac operon. It occurs in a mutant insensitive to catabolite repression. It is established much more rapidly than catabolite repression, and is elicited by glucose analogues that are phosphorylated but not further catabolized by the cell. Thus, transient repression is not a consequence of the exclusion of inducer from the cell, does not require catabolism of the added compound, and does not involve a gross change in RNA metabolism. We conclude that transient repression is distinct from catabolite repression.