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H Ozeki

Publications and source records attributed to H Ozeki.

At least 109 records · Page 6Linked to original sources
PubMed1978

Sequence homology in DNA molecules of temperate phages phi81, phi80 and lambda.

Homology maps between bacteriophages phi81, phi80 and lambda were constructed on the basis of electron microscopy observation of DNA heteroduplexes. In phi81/phi80 heteroduplex, the left half and the right terminal region of 13% the total molecular length were highly homologous, while the remaining region covering the early gene cluster was entirely nonhomologous. In phi81/lambda heteroduplex, high-degree homologies were detected at the left 14% terminal region covering the head gene cluster, the central 3.8% region covering the att-int-xis region and the 1.3% Q homology region. Low-degree homologies of shorter length were scattered at the tail gene cluster, b2 region, cIII region, PQ region and SR region. Comparing our results with the homology maps of other lambdoid phages reported by Simon et al. (1971) and Fiandt et al. (1971), a phylogenic relation of phi81 to other lambdoid phages and the role of recombination in the course of divergence of lambdoid phages are discussed.

Base Sequence↗
PubMed1976

Deletion and amber mutants of fla loci in Escherichia coli K-12.

A rapid screening method for amber fla mutants of E. coli was devised and many mutants were obtained. In addition, strains with deletions of the fla genes in the his-uvrC region were isolated from high-temperature survivors of a lambda cI857 lysogen in which the prophage is located between his and fla. Utilizing these mutants, eleven fla genes (I--XI) and one hag gene were identified in the his-uvrc region, in the following order: his-supD-I-II-(III, IV)-V-(VI, VII)-VIII-IX-hag-(X, XI)-uvrC. The fla genes X and XI and hag are located at about 42.5 min and the other fla genes at about 43.0 min on the E. coli genetic map (Bachmann, Low and Taylor 1976). Mutants of fla gene X showed a slight sensitivity to chi phage, although they lack the flagellar filament.

Chromosome Mapping↗
PubMed1976

Excision and duplication of su3+-transducing fragments carried by bacteriophage phi 80. I. Novel structure of phi 80sus2psu3+ DNA molecule.

DNA molecules of phi 80sus2psu3+ and phi 80dsu3+ isolated by Andoh and Ozeki (1968) were studied by the electron microscope heteroduplex method. The phi 80sus2psu3+ and phi 80dsu3+ DNA lengths were found to be 108.7 and 103.3% of the phi 80 DNA, respectively. The phi 80sus2psu3+/phi 80 heteroduplex shows an insertion loop of 8.7% of the phi 80 DNA which migrates from 7.7 to 9.7%, as measured relative to the left (0%) and right (100%) termini of the mature phi 80 DNA molecule. The region of loop migration occupies the central region of the phi 80 head gene cluster. The presence of su3+-containing Escherichia coli DNA of 6.7% phi 80 unit flanked by two homologous regions of phage DNA of 2.0% of phi 80 unit gives rise to a movable insertion loop. In phi 80dsu3+, from which phi 80sus2psu3+ was derived, 50.5% of the phi 80 DNA at the left arm was replaced by E. coli DNA containing the su3+ gene, equivalent to about 53.8% phi 80 unit in length. The phi 80sus2psu3+/phi 80dsu3+ heteroduplex appears as a double-stranded molecule that bifurcates into two clearly visible single-stranded regions, rejoins, bifurcates, and rejoins again. The middle double-stranded stretches of 6.7% phi 80 unit correspond to the E. coli DNA inserted in phi 80sus2psu3+. Therefore the transducing fragment carried by phi 80sus2psu3+ originates from the inside region of the transducing fragment of defective phage phi 80dsu3+ by at least two illegitimate recombination events.

Chromosome Mapping↗
PubMed1975

Two-dimensional polyacrylamide-gel electrophoresis for purification of small RNAs specified by virulent coliphages T4, T5, T7 and BF23.

RNAs synthesized in Escherichia coli infected with virulent phages T4, T5, T7 and BF23 were labelled with 32PO4 3- after phage infection. [32P]RNAs of low molecular weight were separated by two-dimensional polyacrylamide gel electrophoresis, in which electrophoresis was carried out in two dimensions at different concentrations of acrylamide. The fractionated RNAs were characterized by RNA-fingerprint patterns made after T1 ribonuclease digestion. The two-dimensional gel of 10% yields 20% acrylamide was suitable for RNA of less than 200 nucleotides, while that of 5% yields 10% was preferred for RNAs of about 150--400 nucleotides. With T4 phage, 16 RNA species were separable on a single slab gel. Among those, 11 were identified as the known RNA species, including eight T4 tRNAs, one tRNA precursor and two non-tRNA molecules. In the case of T5 and BF23, more than 20 RNA species were separated on a slab gel; 15 or more RNAs were found in the 4-S RNA region, and several in 5-S and 6-S region. The RNA-fingerprint patterns of many BF23 RNAs were very similar to those of corresponding RNAs of T5. Pseudouridine and ribosylthymidine, minor nucleosides generally present in tRNA, were found in several BF23 4-S RNAs tested. Possibility of those BF23 4-S RNAs as tRNAs is discussed. With phage T7, three RNAs were detected, two of which were much smaller than tRNAs.

Coliphages↗
PubMed1974

Temperature sensitive mutants of Escherichia coli for tRNA synthesis.

An efficient method was devised to isolate temperature sensitive mutants of E. coli defective in tRNA biosynthesis. Mutants were selected for their inability to express suppressor activity after su3(+)-transducing phage infection. In virtually all the mutants tested, temperature sensitive synthesis of tRNA(Tyr) was demonstrated. Electrophoretic fractionation of (32)P labeled RNA synthesized at high temperature showed in some mutants changes in mobility of the main tRNA band and the appearance of slow migrating new species of RNA. Temperature sensitive function of mutant cells was also evident in tRNA synthes: directed by virulent phage T4 and BF23. We conclude that although the mutants show individual differences, many are temperature sensitive in tRNA maturation functions. In spite of much information on the structure and function of transfer RNA (tRNA), our knowledge concerning the biosynthesis of tRNA is relatively poor. It is generally assumed that complete tRNA molecules are made via a series of processing steps from the original transcription products of tRNA genes which are presumably unmodified and longer than mature tRNA molecules. In the case of tyrosine suppressor tRNA of su3(+), an unmodified precursor RNA carrying additional residues at the 3' and 5' ends has been isolated (1,2), and an endonuclease cleaving at the 5' side of this precursor has been identified in E. coli (3). In the case of T4 encoded tRNA, a large precursor molecule for several tRNA's has been reported (4). Some enzymes that catalyze the modifications have also been described (5). However, the over-all picture and the precise mechanisms of tRNA maturation are as yet largely unkown. For study of tRNA biosynthesis in E. coli, a genetic approach may prove useful, as has been the case in other biosynthetic pathways. In order to obtain mutants blocked in any of the intermediary steps of tRNA synthesis, we have developed an efficient selection system that enriches these mutants. Since any mutational block in tRNA biosynthesis might well be lethal, we looked for conditional lethal mutants in which the defect in tRNA synthesis occurs only at high temperature. In this selection system, the su3 gene carried by a temperate phage was newly introduced into cells(su(-)) and those cells incapable of synthesizing su3(+) tRNA at high temperature were selected. Such mutants were easily enriched by using conditions in which cells expressing suppressor activity were killed by two virulent phages. In this communication, we report the method for isolation of mutants and some characterization of tRNA synthesis in these mutants. Recently, Schedl and Primakoff (6) have independently isolated thermosensitive mutants of E. coli defective in tRNA synthesis which may or may not be different types from ours.

Escherichia coli↗