![]() ![]() However, eukaryotic promoters and other gene regulatory sequences may evolve as well. By altering an enzyme, structural protein, or some other factor, the process of mutation can transform functions or physical features. Mutations can occur in genes during DNA replication, and the result may or may not be beneficial to the cell. The evolution of genes may be a familiar concept. Although the process of transcription in eukaryotes involves a greater metabolic investment than in prokaryotes, it ensures that the cell transcribes precisely the pre-mRNAs that it needs for protein synthesis.Įvolution Connection: The Evolution of Promoters Eukaryotic transcription is a tightly regulated process that requires a variety of proteins to interact with each other and with the DNA strand. The processes of bringing RNA polymerases I and III to the DNA template involve slightly less complex collections of transcription factors, but the general theme is the same. The transcription factors systematically fall into place on the DNA template, with each one further stabilizing the preinitiation complex and contributing to the recruitment of RNA polymerase II. The names of the basal transcription factors begin with “TFII” (this is the transcription factor for RNA polymerase II) and are specified with the letters A–J. Basal transcription factors are crucial in the formation of a preinitiation complex on the DNA template that subsequently recruits RNA polymerase II for transcription initiation. Enhancers and silencers affect the efficiency of transcription but are not necessary for transcription to proceed. An army of basal transcription factors, enhancers, and silencers also help to regulate the frequency with which pre-mRNA is synthesized from a gene. The complexity of eukaryotic transcription does not end with the polymerases and promoters. Transcription Factors for RNA Polymerase II These elements bind cellular factors that increase the efficiency of transcription initiation and are often identified in more “active” genes that are constantly being expressed by the cell. Further upstream of the TATA box, eukaryotic promoters may also contain one or more GC-rich boxes (GGCG) or octamer boxes (ATTTGCAT). This sequence is essential and is involved in binding transcription factors. For example, the mouse thymidine kinase promoter also has a conserved CAAT box (GGCCAATCT) at approximately -80. These pseudogenes are copied from mRNA and incorporated into the chromosome. Pseudogenes are genes that have lost their protein-coding ability or are no longer expressed by the cell. The mouse genome includes one gene and two pseudogenes for cytoplasmic thymidine kinase. Would you expect the bacteria to transcribe the gene? A 5' cap and 3' poly-A tail are also added.Ī scientist splices a eukaryotic promoter in front of a bacterial gene and inserts the gene in a bacterial chromosome. \): Eukaryotic mRNA contains introns that must be spliced out.
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