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.