Edward A. Birge

Correlation of 30S ribosomal proteins ofEscherichia coli isolated in different laboratories

SummaryRibosomal proteins isolated from 30S subunits ofE. coli in four laboratories have been correlated by using two-dimensional gel electrophoresis, immunological techniques, amino acid compositions and molecular weights. The results are given in the Table. A common nomenclature for naming 30 S ribosomal proteins and their genetic loci is proposed.

Altered ribosomal protein in streptomycin-dependent Escherichia coli.

We have compared the 30S ribosomal proteins of strains of Escherichia coli sensitive to and dependent on streptomycin and identified a single protein that is functionally altered in the ribosomes dependent on streptomycin. This protein (30S-15) is the same protein that is functionally altered in ribosomes resistant to streptomycin.

Reversion of a streptomycin-dependent strain ofEscherichia coli

SummaryA streptomycin dependent, spectinomycin resistant mutant ofEscherichia coli was used to select spontaneous phenotypic revertants to non-dependence on streptomycin. The ribosomes from one such revertant, which is inhibited by both streptomycin and spectinomycin, were analyzedin vitro. The altered protein responsible for the suppression of the streptomycin dependent phenotype was identified; this protein is 30S-10. The genetic locus for this mutation is a newly identified locus and it has been positioned close to thestr locus. The identification of the altered component responsible for the suppression of the spectinomycin resistant phenotype may be the same as that for the streptomycin dependent phenotype, but this is unproven.

A thermosensitivepdxJ mutation affecting vitamin B6 biosynthesis inEscherichia coli K-12

A temperature-sensitive mutation affecting pyridoxine biosynthesis inEscherichia coli has been isolated following nitrosoguanidine mutagenesis. This is the first report of a conditional mutation affecting that pathway. Three-point transductional analysis and an Hfr mating test indicate that the affected locus ispdxJ and that the gene order isglyA-purI-pdxJ-nadB. The data confirm the present genetic map position ofpdxJ, which had not been accurately determined. Cells carrying the mutation exhibit an absolute requirement for 2.5 μM vitamin B6 when inenbated at temperatures of 38°C or higher.

Genetic map position of the cistron coding for isocitrate dehydrogenase inEscherichia coli K-12

Transductional analysis indicates that theicd cistron, which codes for isocitrate dehydrogenase (E.C. 1.1.1.42), is located between thepurB anddadR cistrons.

Genetics of Temperate Bacteriophages

For all of the bacteriophages discussed in the preceding chapters, a successful phage infection always results in the immediate production of progeny virions. However, many bacteriophages are known for which there is an alternative outcome to phage infection. Instead of the customary unrestrained DNA replication and phage assembly, there is a temperate response in which the bacteriophage sets up housekeeping within the bacterial cell and maintains a stable relationship with that cell and all its progeny for many generations. The varied ways in which the temperate response can be accomplished are the subject of this chapter. The population dynamics of temperate and lytic viruses and their hosts have been analyzed by Stewart and Levin and are not covered here. The physical properties of the temperate bacteriophages discussed in this chapter are summarized in Table 6-1.

The F Plasmid

The discovery of conjugation, although important in its own right, was also significant because it revealed the existence of an unexpected genetic element, the F plasmid. This plasmid, which is the best studied and therefore an excellent example of this interesting group of DNA molecules, will be the subject of this chapter. There are, however, many other types of plasmids which have been discovered, and a representative sample of them will be considered in Chapter 11.

Isocitrate dehydrogenase assays on intact bacterial cells.

A qualitative assay which can be adapted to screen large numbers of Escherichia coli colonies for the presence of soluble enzymes is described. In a test of the system using a new, especially sensitive assay for isocitrate dehydrogenase activity, colonies producing the enzyme could be correctly identified at the 70% level after 2 h of incubation and at the 100% level after 8 h of incubation. The completed reactions are stable for several days at room temperature.

Stimulation of conjugal recombinant production in recB− cells by the subsequent introduction of recB+ genes

SummaryThe introduction of an F′ factor carrying a recB+ gene into F−recB− cells which have just concluded a mating with Hfr cells results in an increased production of recombinant colony forming units involving the Hfr genes. The stimulatory effect approaches the theoretical maximum and does not occur in recB+ recipients. The ability of the F− cells to be stimulated is rapidly lost, although the transcribable recombination product previously reported by Birge and Low (1974) is still producing functional messenger RNA. It is proposed that this is due to the segregation of the recombination products into nonviable cells.

Recombination: Generally and Specifically

The purpose of this chapter is to draw together various aspects of recombination as presented in the preceding chapters and enlarge on the molecular mechanisms involved. The first section presents a summary model for general recombination. Subsequent sections consider site-specific recombination in its various manifestations.