In vitro regulation of DNA-dependent synthesis of Escherichia coli ribosomal protein L12.

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Abstract
The DNA of the transducing phage .lambda.rifd18 contains, among others, the genes for the ribosomal proteins L11, L1, L10 and L12 and the .beta. and .beta.'' subunits of RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6). In a coupled in vitro protein-synthesis system, .lambda.rifd18 DNA directs the synthesis of about 4-5 molecules of L12 per molecule of L10. This is consistent with the finding that there are 4 copies of L12/ribosome. The ratio of L12/L10 was also examined from an EcoRI fragment of .lambda.rifd18 that contains the L10 gene and about 50% of the L12 gene. A significantly lower ratio of truncated L12/L10 was observed compared to the intact phage. The binding of RNA polymerase to various .lambda.rifd18 DNA restriction fragments was used to locate possible promoter sites. These binding experiments suggest that the .beta. and .beta.'' subunits of RNA polymerase are cotranscribed with at least ribosomal protein L12 and, also, that there may be an additional promoter site for the L12 gene within the structural gene for L10.