RNA in Prokaryotes

Polycistronic messenger RNA. In prokaryotes, an RNA that contains two or more cistrons note that only in prokaryotic mRNAs can more than one cis-tron be utilized by the translation system to generate individual proteins. 

Only one RNA polymerase catalyzes the synthesis of all three classes of RNA in prokaryotes. While three RNA polymerases mediate the synthesis of eukaryotic RNA, namely, RNA polymerase I for major rRNA, RNA polymerase II for mRNA, and RNA polymerase III for tRNA (Palmer and Folk, 1990 Woychik and Young, 1990). 

The RNA polymerases evince more sequence specificity than the repair enzymes since they transcribe the information in DNA into specific classes of RNA. In prokaryotes, transcription can be regulated by repressor and related proteins, which are very sensitive to the base sequence in DNA. Similar regulatory requirements undoubtedly exist for the eukaroytic genome but are not as simple. These are discussed subsequently. Regulating proteins combine with certain DNA molecules through recognition of a particular nucleotide base sequence. 

The Shine-Salgano interaction is a base pairing interaction that occurs during translation initiation in prokaryotes between the Shine-Dalgarno sequence on messenger RNA (mRNA) and the anti-Shine-Dalgamo... 

Fig. 5.1. The three domains of life in a radial time sequence based on genetic (RNA) analysis. The distinction between anaerobes and aerobes is not made here and the branching to eukaryotes is left unclear. All the domains advanced with time but in very different ways (see Woese, C. (1998) in Further Reading, and Sogin, M. (1993), Science, 260, 340). Note the general gene transfer in prokaryotes and to eukaryotes (see Chapter 7).

The protein synthesis machinery reads the RNA template starting from the 5 end (the end made first) and makes proteins beginning with the amino terminus. These directionalities are set up so that in prokaryotes, protein synthesis can begin even before the RNA synthesis is complete. Simultaneous transcription-translation can t happen in eukaryotic cells because the nuclear membrane separates the ribosome from the nucleus. 

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