Sequence homology and recombination between the genomes of morphologically dissimilar bacteriophages LP 52 and theta

The lambda - P22 problem

Lambda and P22 are members of 2 families of tailed phages and have limited genomic relationships. Both form hybrids with many phages. P22 appears as a hybrid of mixed ancestry. Despite their similarities, lambda and P22 and their relatives form 2 distinct lineages and must be classified separately.

Correlation of physical maps and some genetic functions in the genomes of the kappa-theta phage family of Bacillus licheniformis

Natural recombinant genomes between several, phenotypically distinct forms of phages kappa and theta were isolated and characterized by DNA restriction fragment mapping and electron microscopic heteroduplex analysis. The phenotypes of the recombinants were correlated with the physical maps of the genomes, and several genetic functions were therefore defined and mapped. All genes necessary for the assembly of infectious virus particles map in a contiguous tract of DNA comprising about 20 kb, or nearly one third of the genome length. No DNA homology occurs within these domains of the two genomes, so that homologous recombination does not take place here and phenotypic mixing of the phages is eo ipso excluded. Other regions of heterology contain regulatory genes responsible for the lytic or temperature character of the phages, and for exclusion of phage kappa by 9.

Three new t-haplotypes of Mus musculus reveal structural similarities to t-haplotypes of Mus domesticus

Three newt-haplotypes,tp 4,tp 12andtp 14, were isolated fromM. musculusmale mice captured in Central and East Bohemia, Czechoslovakia, about 400 km from the zone of hybridization betweenM. musculusandM. domesticusspecies. Complementation tests have shown that all three newt-haplotypes belong totw 73group. When compared with 5t-haplotypes fromM. domesticusthey displayed the same pattern ofBamHI restriction fragments withH-2class I genes, and they also shared thet-specific 5·2 kbTaqI fragment of the alpha globin pseudogene. However, they differed fromM. domesticus t-haplotypes at the D17Leh443 locus since they all displayed a 10·5 kbMspI fragment, labelled by the Tu443 probe, not found in wild type-chromosomes or inM. domesticus t-haplotypes. A hypothesis is proposed thatt-haplotypes inM. domesticusoriginated by a single successful introgression from a parental species during speciation.

Physical mapping of LP51 and LP52 prophages of lysogenic strains of Bacillus licheniformis

The physical maps of the LP51 and LP52 prophages in lysogenic strains of Bacillus licheniformis were constructed on the basis of data obtained by hybridization of phage DNA probes with Southern blots of restricted DNA of the lysogens. The data were compatible with the Campbell model for chromosomal integration; the attP site was mapped at 58.7-61.8 map units of the genomes of both phages. Identification of prophage-host DNA junction fragments indicated the presence of a unique attB site on the bacterial chromosome; the set of junction fragments in the strain B. licheniformis ATCC 10716 was identical to that of ATCC 11946, but different from ATCC 8187. Both the LP51 and LP52 phages used the same integration sites. Upon reinfection with either phage, the cured strains UM12 and UM18 (i.e. 10716 and 11946 cured of LP52 or LP51, respectively) turned out to be integration deficient. In surface cultures the reinfected bacteria could be maintained in the lysogenic state without, however, integrating the phage genome; when these bacteria were passaged in submerged cultures, several modes of anomalous integration were observed, and the phage segregated into a variety of forms, discernible by virulence and plaque morphology. In liquid cultures of UM12(LP51) or UM12(LP52) lytic forms finally predominated, while most lysogenized UM18 were converted into defective lysogens which contained a defective prophage in a stably integrated form.

Denaturation maps of Bacillus licheniformis phages LP52 and theta DNAs

Employing electron microscopy (EM) of partially denatured DNAs of phages LP52 and theta, distinct denaturation maps were determined and correlated with published restriction and heteroduplex maps. The pattern of early melting regions is similar although the two phages share only 50% nucleotide sequence homology.

An electron microscopic heteroduplex study of the sequence relations between the bacteriophages LP52 and theta

The genomes of the phylogenetically related but morphologically distinct bacteriophages LP52 and theta (theta) were compared by electron microscopic heteroduplex analysis. The heteroduplex maps were aligned with known restriction maps. In the heteroduplices of LP52 DNA (63.8 kb) with the DNA of the lytic phage theta c (65.9 kb) the tracts of homologous DNA cover about 50% of the genome length and are interspaced by four large and ten smaller non-base-paired regions. The largest block of non-homologous DNA (18.9 kb), represents the right-hand end and there is an unmatched piece of DNA at the left-hand end as well. Most of the heterology is due to substitution resulting in the conservation of the total length of DNA; the three insertions/deletions amount to less than 3.2% of the genome length. Heteroduplices between the DNAs of phage LP52 and the temperate phage theta 1 (65.0 kb) resembled those of LP52:theta c except for the absence of minor loops. Heteroduplex theta c:theta 1 displayed about 9% heterology in seven separate loops which coincided with sections of diversity on the restriction maps; 4.8% of theta 1 DNA did not hybridize with either theta c or LP52 DNA.