Formation of various genome lengths of hybrids between the serologically and morphologically unrelated bacteriophage species

Hybrids between rubella virus and a latent virus of baby hamster kidney cell line BHK21: characterization of rubella virus and type 2 hybrid virus genomes and determination of their physical homology

The biochemical nature of rubella virus and type 2 hybrid virus, which is a recombinant between rubella virus and a latent retrovirus of BHK21 cells, has been characterized. Type 2 hybrid virus carries DNA polymerase able to copy exogenous DNA. However, disrupted type 2 hybrid virions do not synthesize detectable amounts of DNA using the endogenous viral RNA or synthetic poly(rA)/oligo(dT) primed as a template. Thus, the type 2 hybrid virus DNA polymerase has no detectable reverse transcriptase activity. Rubella virus and type 2 hybrid virus RNA can serve as templates for avian myeloblastosis virus (AMV) reverse transcriptase, although they are inefficient. The addition of oligo(dT) to these viral RNA showed no significant stimulation of their template activity for AMV reverse transcriptase. The oligo(dT)-cellulose affinity column bound neither rubella virus nor type 2 hybrid virus RNA. This suggests that both RNA genomes have a very short poly(A) tail at their 3' end. Thus, complementary DNA (cDNA) synthesis by AMV reverse transcriptase using oligo(dT) primers showed no preferential reverse transcription from the genomic 3' terminus and produced only short cDNA fragments (about 200 nucleotides). We cross-hybridized these short cDNA fragments with their viral RNA, assuming that they are copies of random sites of the genome. These cDNA-RNA hybridization analyses of physical homology between type 2 hybrid virus and rubella virus genomes revealed that about 70% of the type 2 hybrid virus genome is derived from about an 85% portion of the rubella virus genome. These values indicate that the size of the type 2 hybrid virus genome is about 21% larger than that of the rubella virus genome. Co-sedimentation studies of these viral RNA by sucrose density gradient centrifugation confirmed that the molecular weight of type 2 hybrid virus RNA is 20% higher than that of rubella virus RNA. We propose a genomic structure of the type 2 hybrid virus taking into account both physical and biochemical data.

Genomic structure of phage F22, a hybrid between serologically and morphologically unrelated Salmonella typhimurium bacteriophages P22 and Fels 2

Salmonella typhimuriumphage P22 can recombine with a serologically and morphologically unrelated Salmonella phageFels 2to yield the hybrid phage F22 at a frequency of about 10−12. F22 has inherited the entire late genes (protein coat and tail structural genes) ofFels 2but carries some P22 early genes. P22 genes in the F22 phage were indentified by marker rescue of various P22 mutants. The F22 genome carries thex-erf-c-18-12segment of the P22 genome. A number of P22 amber mutants were also tested to support these data. The F22 region homologous to P22 was mapped by scoring the ratio of P22 backcross recombinant types in lysates of F22 lysogens superinfected with P22c2ts12. The ratio of the distances between these markers and the ends of the homologous region was determined. Furthermore a new F22 hybrid designated F22dis, containing both P22 immunity regions (candIm), was isolated at a frequency of about 10−4by superinfecting F22 lysogens with P22. F22disphage has lost someFels 2gene(s) which have been replaced by the P22 segment containing theImregion, resulting in formation of a defective hybrid phage.