Thermal dissociation of synthetic lambda (λ) RNA- Escherichia coli DNA hybrids

Abstract

The possible existence of nucleotide sequence complementarity between the temperate phage lambda (λ) and its host, Escherichia coli, was examined by means of thermal dissociation studies of RNA-DNA hybrids. Radioactive λ RNA and T4 RNA were synthesized “in vitro” using the DNA-dependent RNA polymerase. RNA-DNA hybrids were formed between λ RNA and λ DNA, T4 RNA and T4 DNA, and λ RNA and E. coli DNA. The λ RNA-λ DNA hybrid dissociated over the same temperature range as the λ RNA- E. coli DNA hybrid. This range was considerably broader than that exhibited by the T4 RNA-T4 DNA complex. Correlation of the shape and average dissociation temperature ( T M ) 4 4 The following abbreviations will be used: T M = temperature at which half the RNA has dissociated from DNA; 1 × SSC = 0.15 M NaCl, 0.015 M sodium citrate; A-T and G-C = adeninethymine and guanine-cytosine base pairs, respectively. of the melting curves of the RNA-DNA hybrids with those previously reported for λ DNA and T4 DNA provides physical evidence that nucleotide sequence complementarity exists between primer DNA and the synthetic RNA product. It is also possible to conclude that complementarity exists between λ DNA and E. coli DNA. The broad range of dissociation temperatures for the λ RNA-λ DNA and λ RNA- E. coli DNA hybrids demonstrates the presence of a relatively large amount of intramolecular chemical heterogeneity in λ DNA.