Single Transcriptional Unit Research Articles

Transcriptional mapping of vesicular stomatitis virus in vivo

Synthesis of the proteins of vesicular stomatitis virus (Indiana serotype) was studied in mouse L cells infected with virus that had been exposed to UV radiation. The UV target sizes measured during primary transcription indicated that the five genes occupy a single transcriptional unit. Thus, in infected cells, as a cell-free system, transcription of vesicular stomatitis virus RNA initiates at a single point and proceeds in the order N. NS, M, G, and L.

Identification of two copies of the gene for the elongation factor EF-Tu in E. coli.

Two copies of the structural gene for the elongation factor EF-Tu have been identified in Escherichia coli: one near rif and the other near str. The latter seems to belong to a single transcriptional unit together with the genes for ribosomal protein S7, S12 (str) and the elongation factor EF-G (fus).

Coordinate and differential in vitro syntheses of two RNA polymerase subunits.

THE β subunit of Escherichia coli RNA polymerase—one of three subunit types (α, β, β′) in the enzyme core structure—is specified by a genetic locus, rif(ref. 1). Specialised transducing phages which carry the rif region have been isolated2,3. If DNA is extracted from these phages, it can be used to direct the synthesis of the β subunit in vitro in a coupled transcription/translation system4,5. It has been suggested that other RNA polymerase structural genes may also be in this region of the chromosome6. Recent genetic evidence shows that the β and β′ subunits are produced from a single transcriptional unit in vivo7. DNA extracted from three independently isolated rif transducing phages however, failed to direct the synthesis of any detectable β′ molecules in vitro in the coupled systems previously described4,5 (Fig. 1a). Here I describe a coupled system which synthesises β and β′ in vitro with equal efficiency from rif transducing phage DNA.

Transcription unit mapping in bacteriophage T7. I. In vivo transcription by Escherichia coli RNA polymerase.

Premature termination of transcription at UV lesions in DNA permits a study of the sequential order of transcription by E. coli RNA polymerase of the genes in the early region of T7. This analysis is extended to the transcription by E. coli polymerase of the late region of T7 by deleting the early terminator. The results demonstrate the existence of a single large transcription unit spanning the early region, with a promotor located at the left end of the T7 genome. Furthermore, there are no initiation sites for E. coli RNA polymerase in the late region. When E. coli polymerase transcribes the late region, it does so exclusively by initiation at the early promotor.