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Function of Genetic Material

Gene Structure, Gene Function, and Genetic Regulation of Metabolism in Bacteria and Fungi

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Part of the book series: Progress in Botany / Fortschritte der Botanik ((BOTANY,volume 44))

Abstract

The trp operon of E. coli consists of a promoter/operator region followed by a 162-base pair stretch before the ATG initiation of the first of altogether five contiguous cistrons each coding for a different protein (Fig. 1). Transcription of all five cistrons leads to a single messenger-RNA molecule. This molecule contains the 162-base “leader sequence”. All five proteins are formed in equimolar amounts. The regulatory range between full expression and full repression covers a factor of about 600. Early on, it was observed that the first 140 base pairs of the leader sequence, trpL, were transcribed 8–10 times more frequently than the coding regions of the operon. Therefore, there must be a site where transcription initiated at the promoter/operator sequence was terminated before reaching the coding sequences of the operon. This termination was called attenuation and found to be influenced by the supply of tryptophan to the cells. Most important was the isolation of mutants with deletions in the leader sequence where no attenuation took place (reviewed by CRAWFORD and STAUFFER*, 1980). A more recent observation of WINKLER and YANOFSKY (1981) was made in an in vitro transcription system. Normally there are two transcripts, the full-length transcript and the 140-base leader transcript.

Sequencing of bacterial genes has provided enough data to search for generally used regions determining promotion and termination of transcription. However, as pointed out in a review (Rosenberg and Court, 1980), “it remains extremely difficult (if not impossible) to predict from structural information alone which regions of DNA will be recognized by RNA polymerase as either promoter or terminator signals”. As will be described below, this also applies to eukaryotic gene sequences. Further complexities are added by attenuation and pausing. To demonstrate these two principles, regulation of gene expression will be described in detail for the trp operon of Esoherichia coli following an extensive description of Yanofsky*1 (1981) and a short presentation of Watson (1981).

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© 1982 Springer-Verlag Berlin Heidelberg

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Zimmermann, F.K. (1982). Function of Genetic Material. In: Ellenberg, H., Esser, K., Kubitzki, K., Schnepf, E., Ziegler, H. (eds) Progress in Botany / Fortschritte der Botanik. Progress in Botany / Fortschritte der Botanik, vol 44. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-68752-5_16

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  • DOI: https://doi.org/10.1007/978-3-642-68752-5_16

  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-642-68754-9

  • Online ISBN: 978-3-642-68752-5

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