Construction in vitro of hybrid plasmids carrying all the EcoRI fragments from lambdarifd18 DNA.

The cloning of all the eleven fragments obtained by degrading the phage lambdarifd18 by the restriction enzyme EcoRI into the plasmid pSF2124 has been achieved: nine of these fragments have been cloned individually, whereas two others have been cloned jointly in the same plasmid. These fragments harbor, in addition of lambda genes, the genes for ribosomal proteins, the elongation factor Tu, the beta and beta' subunits of RNA polymerase and the ribosomal RNAs. The clones carrying the ribosomal RNA genes have been constructed to provide convenient plasmids to determine the primary structure of ribosomal RNAs. Some further genetic manipulations in vitro have been performed on two of them to remove extraneous non-ribosomal RNA gene sequences; the ribosomal genes purified this way have been subcloned into the plasmid pBR322. Other clones of interest have been obtained which carry the genes for the elongation factor Tu, a number of 50-S ribosomal proteins and the beta subunit of RNA polymerase.