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P J Highton

Publications and source records attributed to P J Highton.

13 recordsLinked to original sources
PubMed1990

Evidence for the exchange of segments between genomes during the evolution of lambdoid bacteriophages.

Heteroduplexes between the DNA molecules of 12 lambdoid phages were analysed by electron microscopy. The positions of the regions of base sequence homology between the DNA molecules divide them into 35 segments, most of which have a number of alternative forms (alleles), which in general must be functionally homologous but which differ in base sequence and length. The positions of the boundaries between segments in phage lambda show that each segment is probably a gene or a group of genes, and that each phage genome is a different combination of the alleles of the segments. The frequency of the occurrence of the different alleles indicates that the total number in the natural population may be small. The different combinations of alleles of separate segments, found among the phages, indicate the exchange of segments between the phages during their evolution.

Alleles↗
PubMed1985

Evidence that the outer membrane protein gene nmpC of Escherichia coli K-12 lies within the defective qsr' prophage.

Recombinants between phage lambda and the defective qsr' prophage of Escherichia coli K-12 were made in an nmpC (p+) mutant strain and in the nmpC+ parent. The outer membrane of strains lysogenic for recombinant qsr' phage derived from the nmpC (p+) strain contained a new protein identical in electrophoretic mobility to the NmpC porin and to the Lc porin encoded by phage PA-2. Lysogens of qsr' recombinants from the nmpC+ strain and lysogens of lambda p4, which carries the qsr' region, did not produce this protein. When observed by electron microscopy, the DNA acquired from the qsr' prophage showed homology with the region of the DNA molecule of phage PA-2 which contains the lc gene. Relative to that of the recombinant from the nmpC (p+) mutant, the DNA molecule of the recombinant from the nmpC+ parent contained an insertion near the lc gene. These results were supported by blot hybridization analysis of the E. coli chromosome with probes derived from the lc gene of phage PA-2. A sequence homologous to the lc gene was found at the nmpC locus, and the parental strains contained an insertion, tentatively identified as IS5B, located near the 3' end of the porin coding sequence. We conclude that the structural gene for the NmpC porin protein is located within the defective qsr' prophage at 12.5 min on the E. coli K-12 map and that this gene can be activated by loss of an insertion element.

Bacterial Outer Membrane Proteins↗
PubMed1972

Penicillin and cell wall synthesis: a study of Bacillus cereus by electron microscopy.

The changes in wall structure of a penicillinase micro-constitutive strain of Bacillus cereus (569/H/24), on exposure to penicillin, and after its removal by addition of penicillinase, have suggested the following model for the growth of the walls of these cylindrical cells. Longitudinal extension is by addition of material to a large and continuously increasing number of growing points uniformly distributed over the cylindrical surface. Addition is only in the longitudinal direction so that the cell diameter remains constant. Cross walls grow by addition to their inner edge, and on completion the two new rounded ends of the daughter cells are formed by splitting at the outer edge and continued addition at the center. The ends are conserved.

Bacillus cereus↗
PubMed1971

Penicillin and cell wall synthesis: a study of Bacillus licheniformis by electron microscopy.

The changes in wall structure of two penicillinase-negative strains of Bacillus licheniformis on addition of penicillin were studied. After addition of penicillin to give a concentration of 1 unit/ml, exponentially growing cells of strain 749 c/72 doubled once and then stopped. Strain 749c/72/IIIg was more resistant and continued growing, but synthesis appeared to become uncontrolled over the surface, producing localized wall thickening at the expense of elongation, and leading to distorted cells and growth in twisted and coiled chains, with an accompanying drop in growth rate. The continued growth can be explained by the existence of a less sensitive transpeptidase, but there is no obvious explanation for the uncontrolled synthesis. The effect of penicillin could be reversed by addition of penicillinase in both strains, although there appeared to be a persistent effect of penicillin which also produced distorted cells for a few generations and inhibited cell separation. The changes in wall structure produced by penicillin and penicillinase appeared all over the cell surface, suggesting that wall synthesis occurred all over the cell. Also a separate process for cross-wall synthesis is suggested since this appeared less sensitive than wall synthesis.

Bacillus↗