Elongation of RNA Transcripts

Irinotecan is a topoisomerase-I inhibitory agent that prevents the initiation and elongation of RNA transcription, DNA replication, and supercoiling of DNA (44). Investi-... 

Elongation of the transcript occurs by incorporation of ribonucleotides to create a copy or RNA complement of the DNA template. 

To enable RNA polymerase to synthesize an RNA strand complementary to one of the DNA strands, the DNA duplex must unwind over a short distance, forming a transcription bubble. During transcription, the E. coli RNA polymerase generally keeps about 17 bp unwound. The 8 bp RNA-DNA hybrid occurs in this unwound region. Elongation of a transcript by E. coli RNA polymerase proceeds at a rate of 50 to 90 nucleotides/s. Because DNA is a helix, movement of a transcription bubble requires considerable strand rotation of the nucleic acid molecules. DNA strand rotation is restricted... 

Alternative Sigma Factors Trigger Initiation of Transcription at Different Promoters Elongation of the Transcript Termination of Transcription Comparison of Escherichia coli RNA Polymerase with DNA Poll and PolIII... 

General transcription factors (GTFs) help to localize the RNA polymerase correctly on the promotor and to form a transcription-competent initiation complex. They serve to impose a specific structure on the transcription start site, and some of them are required for elongation of the transcript. 

Cyclin T-CDK9 (review Simone and Girodano, 2001) functions as a positive transcription factor during transcription elongation of RNA polymerase II by phosphor-ylating the CTD. The HIV regulatory protein Tat binds to and specifically activates the cyclin T-CDK9 complex. 

Other steps of RNA synthesis such as elongation or termination also control the abundance of proteins. These are less well understood than the initiation of transcription described here. 

The general topology of rubredoxins is also observed in the general zinc-ribbon motif in RNA polymerases or in transcription factors (59). The first published zinc-ribbon structure was that of the nucleic-acid binding domain of human transcriptional elongation factor TFIIS (PDB file ITFI) 40). These zinc binding domains and rubredoxins... 

F ig U re 1 3.1 A schematic view of RNA chain elongation catalyzed by an RNApolymerase. In the region being transcribed, the DNA double helix is unwound by about a turn to permit the DNAs sense strand to form a short segment of DNA-RNA hybrid double helix. That forms the transcription bubble. Note that the DNA bases in the bubble on the antisense strand are now exposed to the enzyme and are useable as a template for chain elongation. The RNApolymerase works its way down the DNA molecule until it encounters a stop signal. (Reproduced from D. Voet and J. G. Voet, Biochemistry, 3rd, edn, 2004 Donald and Judith G Voet. Reprinted with permission of John Wiley and Sons, Inc.)... 

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