What is the biological significance of having two different types of terminators in transcription?
Transcription in prokaryotes is terminated by factors called rho-dependent and rho-independent terminators; Rho is a ring-shaped protein and is the main factor required for termination (Leland, 2010). The rho-dependent and rho-independent terminators play a major role in the separation of an RNA transcript from the DNA template which signifies the end of transcription. However, the exact process is not completely understood yet. The rho-independent terminator is typically encoded in the genome and is positioned downstream from the stop codon. There is definitely a difference in structure between the two terminators; rho-independent terminators contain an inverted and repeated sequence which is able to form a hairpin structure and I will discuss the structure of a rho-dependent terminator shortly. The sequence within the loop in the rho-independent terminator is partly species specific. For example, the hairpin loops in E. Coli may contain the sequence GAAA or TTCG while the sequence in other species like B. subtilis may be TTT or AAAA to name a few. This may deduce one reason why we have two different terminators in transcriptions; in order to account for the magnitude of the number of species on Earth, especially in the prokaryote section. On the other hand, rho-dependent terminators were first learned about in bacteriophage genomes and are widespread in the bacteria species. The mechanism for the rho-independent terminator to end transcription occurs when the separation of the transcriptional elongation complex is more beneficial than continuing, largely due to the increasing instability (Ciampi, 2006). These types of terminators can be found at the ends of genes and they play a significant role in controlling gene expression. For example, there exists a rho-dependent terminator that is involved in the expression of the damaging tryptophanase (tna) operon of E....
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