Transcription Regulation in Prokaryotes

Although many RNAs and proteins are produced in even a simple prokaryotic cell, not all of them are produced at the same time or in the same quantities. In prokaryotes, the control of transcription is largely responsible for controlling the level of protein production. In fact, many equate transcription control with gene expression. 

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Picard, E., Dressaire, C., Girbal, L., and Cocaign-Bousquet, M. (2009) Examination of post-transcriptional regulations in prokaryotes by integrative biology. C R Biol 332, 958—973. 

Regulationof gene expression in eukaryotes proceeds primarily by control of transcription as in prokaryotes. Some systems are also regulated at the translational level. 

More complex transcriptional regulation. Like prokaryotes, eukaryotes rely on conserved sequences in DN A to regulate the initiation of transcription. But prokaryotes have only three promoter elements (the —10. -33. and UP elements), whereas eukaryotes use a variety of types of promoter elements, each identified by its own conserved sequence. Not all possible types will he present together in the same promoter. n eukaryotes, elements that regulate transcription can be found at a variety of locations in DNA, upstream or downstream of the start site and sometimes at distances much farther from the start site than in prokaryotes. For example, enhancer elements located on DNA far from the start site increase the promoter activity of specific genes. 

Transcription is tightly regulated. In prokaryotes, only about 3% of the genes are undergoing transcription at any given time. In a differentiated eukaryotic cell, it is approximately 0.01%. 

Protein methylation is one of the most common protein modifications found in a wide range of prokaryotic and eukaryotic proteins that are involved either in regulation of transcription or in translation. Several amino acids can be modified, mainly by either N-methylation or C-methylation. Protein methylation has been... 

C. Eukaryotic gene regulation is much more complex than in prokaryotes, with expression dependent on several types of transcription factors as well as chromatin structure. 

We begin by examining the interactions between proteins and DNA that are the key to transcriptional regulation. We next discuss the specific proteins that influence the expression of specific genes, first in prokaryotic and then in eukaryotic cells. Information about posttranscriptional and translational regulation is included in the discussion, where relevant, to provide a more complete overview of the rich complexity of regulatory mechanisms. 

The effects of chromosome structure on gene regulation in eukaryotes have no clear parallel in prokaryotes. In the eukaryotic cell cycle, interphase chromosomes appear, at first viewing, to be dispersed and amorphous (see Figs 12-41, 24-25). Nevertheless, several forms of chromatin can be found along these chromosomes. About 10% of the chromatin in a typical eukaryotic cell is in a more condensed form than the rest of the chromatin. This form, heterochromatin, is transcriptionally inactive. Heterochromatin is generally associated... 

In the previous chapter we discussed DNA-binding proteins that regulate transcription in prokaryotes. The principles that govern recognition between proteins in eukaryotes show some similarities and some differences. In both cases specific recognition is dominated by interactions that take place in the major groove of the DNA. The specific interactions usually involve H bond formation... 

Further details of the nature and regulation of transcription in prokaryotes and eukaryotes and the post-transcriptional processing of mRNA transcripts are given in Chapter 9. 

Transcription and transcriptional regulation is more complicated in eukaryotes than in prokaryotes. The very much larger amount of DNA in eukaryotes is organized with histones... 

Copper ion homeostasis in prokaryotes involves Cu ion efflux and sequestration. The proteins involved in these processes are regulated in their biosynthesis by the cellular Cu ion status. The best studied bacterial Cu metalloregulation system is found in the gram-positive bacterium Enterococcus hirae. Cellular Cu levels in this bacterium control the expression of two P-type ATPases critical for Cu homeostasis (Odermatt and Solioz, 1995). The CopA ATPase functions in Cu ion uptake, whereas the CopB ATPase is a Cu(I) efflux pump (Solioz and Odermatt, 1995). The biosynthesis of both ATPases is regulated by a Cu-responsive transcription factor, CopY (Harrison et al., 2000). In low ambient Cu levels Cop Y represses transcription of the two ATPase genes. On exposure to Cu(I), CopY dissociates from promoter/operator sites on DNA with a for Cu of 20 jlM (Strausak and Solioz, 1997). Transcription of copA and copB proceeds after dissociation of CuCopY. The only other metal ions that induce CopY dissociation from DNA in vitro are Ag(I) and Cd(II), although the in vivo activation of copA and copB is specihc to Cu salts. The CuCopY complex is dimeric with two Cu(I) ions binding per monomer (C. T. Dameron, personal communication). The structural basis for the Cu-induced dissociation of CopY is unknown. Curiously, CopY is also activated in Cu-dehcient cells, but the mechanism is distinct from the described Cu-induced dissociation from DNA (Wunderh-Ye and Solioz, 1999). 

Pennella MA, Giedroc DP. Structural determinants of metal selectivity in prokaryotic metal-responsive transcriptional regulators. BioMetals 2005 18 413-428. 

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