Coding of stable 4S RNA molecules by the resistance factor R1

With the aid of DNA-RNA hybridization experiments it was shown that an E. coli strain harbouring the resistance factor R1 contains small, stable RNA species which are capable of annealing with the DNA of this R-factor. At a higher hybridization temperature RNA molecules form the isogenic, sensitive strain could also hybridize to the R1-DNA. These RNA-species were again detected if the RNA was extracted from P. mirabilis carrying this plasmid. The fact that sulfur-labelled RNA also hybridized to the plasmid DNA seems to indicate that some of these molecules are tRNAs.