Mutations in the uncE gene affecting assembly of the c-subunit of the adenosine triphosphatase of Escherichia coli.

The amino acid substitutions in the mutant c-subunits of Escherichia coli F1F0-ATPase coded for by the uncE429, uncE408 and uncE463 alleles affect the incorporation of these proteins into the cell membrane. The DNA sequence of the uncE429 allele differed from normal in that a G leads to A base change occurred at nucleotide 68 of the uncE gene, resulting in glycine being replaced by aspartic acid at position 23 in the c-subunit. The uncE408 and uncE463 mutant DNA sequences were identical and differed from normal in that a C leads to T base change occurred at nucleotide 91 of the uncE gene, resulting in leucine being replaced by phenylalanine at position 31 in the c-subunit. An increased gene dosage of the uncE408 or uncE463 alleles resulted in the incorporation into the membranes of the mutant c-subunits. The results are discussed in terms of the 'Helical Hairpin Hypothesis' of Engelman & Steitz [(1981) Cell 23,411-422].     

Thecal ultrastructure ofScrippsiella faeroense

Summary The thecal ultrastructure ofScrippsiella faeroense (Paulsen) Balech and Oliveira Soares as seen in the electron microscope is described. Additional structural detail of the thecal plate surface, plate connections, and the apical pore, is revealed.     

Conditional Mutator Gene in Escherichia coli: Isolation, Mapping, and Effector Studies

A mutator gene, mutD5, whose phenotype is conditional, has been identified in Escherichia coli. By P1 transduction it has been shown to lie at about 5.7 min on the chromosome, being co-transduced with proA and argF. In rich medium, streptomycin- and nalidixic acid-resistant mutation frequencies are 50 to 100 times higher than those in minimal medium. In minimal medium, the mutD5-induced mutation frequencies are still 50 to 100 times above co-isogenic wild-type (mut(+)) levels. Similar results were obtained with all markers tested. Mutant frequencies can be raised by thymidine in the medium at concentrations as low as 0.04 muM, or by the endogenous generation of thymidine from thymine plus a deoxyribosyl donor. Deoxyadenosine, various ribonucleosides, thymine, and 2-deoxyribose do not stimulate mutation. None of these effects are related to growth rate, since growth rate and mutation rate can be decoupled completely.     

Selection for High Mutation Rates in Chemostats

Complementation and polarity suppression data are interpreted in terms of the genetic structure of the maltose B region. It is proposed that this region comprises two divergent operons. One operon includes malK, a cistron involved in maltose permeation, and lamB the only known cistron specifically involved in lambda receptor synthesis. The other operon includes malJ(1) and malJ(2) which are most probably two different cistrons, both involved in maltose permeation*. It is further assumed that expression of the two operons is controlled by malT, the positive regulatory gene of the maltose system, located in the malA region. The target(s) for the action of the malT product is (are) most likely to be located between malJ(1) and malK. There is an indication that the two operons might overlap in the region of their promoters. The structure of such an overlap as well as the possible function of the products of the different cistrons in malB are briefly discussed.     

Carnitine and trimethylaminobutyrate synthesis in rat tissues (Short Communication)

Liver and testis slices convert 6-N-trimethyl-lysine into 4-N-trimethylaminobutyrate and carnitine. Adipose, skeletal muscle, heart, or kidney tissues metabolize trimethyl-lysine into trimethylaminobutyrate but not into carnitine. Trimethylaminobutyrate hydroxylation, forming carnitine, occurs in liver and to a minor degree in testis. Liver is the primary site of carnitine biosynthesis in the rat.     

Purification, Ultrastructure, and Composition of Axial Filaments from Leptospira

The ultrastructure of three strains of water Leptospira was studied by negative staining, thin sectioning, and freeze-etching. The cells possessed a triple-layered sheath which covered two independent axial filaments, one inserted subterminally in each end of the cell. The protoplasmic cylinder was surrounded by a triple-layered cell wall and possessed ribosomes, lamellar structures, and a typical procaryotic nuclear region. The axial filament was comprised of several component structures. An axial fibril, with a diameter of 20 to 25 nm, consisted of a solid inner core (13 to 16 nm in diameter) surrounded by a coat. A terminal knob (40 to 70 nm in length) was connected to a series of disc insertion structures at the terminal end of the axial fibril. The axial fibril was surrounded by a helical outer coat (35 to 60 nm in diameter) which was composed of a continuously coiled fiber, 3 to 4 nm in diameter, embedded in an electron-dense material. A procedure for the purification of the axial fibrils was presented and their ultrastructural, physical, and chemical properties were determined. Similarities in ultrastructural, physical, and chemical properties were noted between the axial fibrils and bacterial flagella. A schematic model of the leptospiral axial filament is presented, and a mechanism is proposed for its function as a locomotor organelle.     

Mutator Gene Studies in Escherichia coli

An Escherichia coli mutator gene, mutT, has been shown by P1-mediated crosses to map between the leucine and azide loci. The mutT1 and azi-r alleles cotransduce with a frequency of >92%. In mutT1/mutT⁺ merodiploids, the mutT1 phenotype is recessive; in mutT1/F′trp or mutT1/F′lac merodiploids, the mutT1 allele has a trans effect. The gene can mutate λ and T7 phage but not T1, T3, T4, T5, and S13.