[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fpnO90BktZD-AtVPwo17KI0-TEHWKtKr56ZR6pr_zznQ":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":47},[4,8,12,16,20,24,28],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":46},"dna-transcription","DNA Transcription: Steps and Mechanism",null,"Sushmita Baniya","2022-07-11","2025-12-29",false,"molecular-biology","The synthesis of the single-stranded RNA, complementary to one of the DNA strands is called transcription. The genetic information encoded in the double-stranded DNA is transformed into the RNA strand by the action of the enzyme RNA polymerase. Transcription produces three [types of RNA](\u002Ftypes-of-rna-structure-and-functions\u002F): messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).\n\n- mRNA: carries instruction for protein synthesis\n- tRNA: transports the aminoacids\n- rRNA: component of the ribosomes\n\n> Among these three types of RNA, only messenger RNA (mRNA) is translated into proteins.\n\nDouble-stranded is made up of two single strands. Each of these strands has its function. One strand is the **template strand (non-coding strand, antisense strand)**, and another is the **non-template strand (coding strand, sense strand)**. The template strand serves as a template for RNA synthesis, i.e., if adenine (A) is encoded in the template strand, uracil (U) will be encoded in the newly synthesized RNA. If guanine (G) is encoded in the template strand, then cytosine (C) will be encoded in the RNA.\n\n![ - Template and coding strandSource:https:\u002F\u002Fwww.lecturio.com\u002Fconcepts\u002Fstages-of-transcription\u002F](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Ftemplate-strand.png)Figure: Template and coding strandSource:https:\u002F\u002Fwww.lecturio.com\u002Fconcepts\u002Fstages-of-transcription\u002F\n\n## Steps in Transcription (RNA synthesis)\n\nTranscription in prokaryotes (e.g., *E. coli*) is divided into three steps: initiation, elongation, and termination.\n\n### Initiation\n\nTranscription begins by binding the RNA polymerase holoenzyme to the promoter region in DNA. The promoter region is the specific sequence in the DNA that is the initiation site for transcription.\n\n![RNA polymerase holoenzyme - RNA polymerase: Holoenzyme](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Fholoenzyme.png)Figure: RNA polymerase: Holoenzyme\n\nRNA polymerase consists of multiple subunits. It consists of core enzyme and holoenzyme. The RNA polymerase helps in unwinding the DNA double helix. Then one of the strands functions as a template.\n\n- **Core enzyme** consists of 2α, β and β’. The core enzyme lacks specificity and cannot recognize the promoter region of the DNA template.\n- **Holoenzyme** is made up of 𝛔-subunit plus the core enzyme. The 𝛔- subunit (‘sigma factor ) helps the RNA polymerase to recognize the promoter region on the DNA.\n\n#### Promoter region\n\nIn *E.coli*, RNA polymerase binds within a region stretching from about 70 base pairs (bp) before the transcription starts sites to about 30 bp after it. The first base at the transcription start site is “+1,” but none of the bases is designated “0”.\n\nThe promoter region extends between compositions -70 and +30. The 𝛔-subunit in the RNA polymerase recognizes the promoter site. The sequences that the sigma factor recognizes in the promoter site are called the **Pribnow box**.\n\n![pribnow box tata box - Pribnow box](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FPribnow-box.png)Figure: Pribnow box\n\n**Pribnow box** is located to the left of the transcription start site at -10 regions. The six nucleotides (5’- **TATAAT**– 3’ or **TATA** box) are present in it.\n\n**-35 sequence** is located at 35 bases to the left of the transcription start site. The nucleotide sequence (5’-**TTGACA**-3’) is present in it.\n\n#### Binding\n\n![Binding of RNA polymerase - Binding of RNA polymerase, Source: Pearson Education](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Felongation-fig.png)Figure: Binding of RNA polymerase, Source: Pearson Education\n\nRNA polymerase recognizes and binds the promoter region in the DNA. Initially, it forms the closed complex in which the DNA is intact. Later it forms the open complex in which DNA starts to unwind with the action of the RNA polymerase enzyme. Unwinding occurs near the -10 sequence or the TATA box because there are no sufficient GC nucleotide pairs, and has weak bonding in this region. Separation of the two DNA strands takes place over 17 bp segments. The bases present in the coding strand are exposed, allowing the synthesis of the RNA by adding the ribonucleoside triphosphates.\n\n### Elongation\n\nRNA polymerase starts to synthesize a transcript of the DNA sequence and does not need primer either. Usually, purine ribonucleotide is added in the beginning. As the RNA strand synthesizes, an RNA-DNA hybrid helix (8-9 nucleotides) is formed. The total structure is called a **transcription bubble.** The sigma subunit is released after the formation of the DNA-RNA hybrid.\n\nThe polymerase leaves the promoter and functions to elongate the RNA. The sigma subunit needs to be released to elongate the RNA because it blocks the RNA exit channel. Then core enzyme of the RNA polymerase moves along the DNA template to the termination point for the elongation of the RNA. To join the ribonucleotides, a phosphodiester bond is formed. The ribonucleotides Adenine (A), Uracil (U), Guanine (G), and Cytosine (C) are added to the growing chain. Pyrophosphate is released whenever a ribonucleotide is added. DNA topoisomerases I and II relax the supercoils which may be formed during the elongation process.\n\n### Termination\n\nRNA chain keeps on elongating until it reaches the termination point.There are two types of termination: rho (**⍴)** dependent termination and rho independent termination.\n\n#### Rho-dependent termination\n\nRho (⍴)protein is required to release the RNA product. Rho protein neither binds to the RNA polymerase nor the DNA. It binds tightly to RNA, where it reaches the RNA polymerase-DNA complex. Rho is an ATP-dependent RNA-stimulated helicase that disrupts the nascent RNA-DNA complex. Rho protein binds the C-rich region near the 3’ end of the newly synthesized RNA and migrates till it finds the termination site in the 5’-3’ direction.\n\nWhen it reaches the termination site, RNA and RNA polymerase are released from the DNA. Hence the transcription is terminated in it.\n\n#### Rho-independent termination\n\nIt does not require rho protein. The RNA polymerase can recognize termination signals, i.e., GC-rich sequence on the DNA template. It consists of the inverted repeat with the central non-repeating segment.\n\n![Rho independent termination - Rho-independent termination](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Finverted-repeats.png)Figure: Rho-independent termination\n\nIn the newly formed RNA, intra-strand base pairing occurs by folding back on themselves. Then it forms the hairpin loop-like structure. The A sequences follow this loop structure in the DNA template. So the complementary base pair in the RNA will be U sequences in the RNA. The binding of the UA is weak because it contains only two hydrogen bonds in U=A. Similarly, at the base of the stem, the GC-rich region stabilizes the secondary structure of the hairpin.\n\nWhen the synthesis of the RNA molecule is terminated, the enzyme separates from the DNA template. It then dissociates to the free core enzyme and free rho factor.\n\n![Rho independent termination - Rho-independent terminationSource: https:\u002F\u002Fwww.biolearners.com](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Frho-independent.png)Figure: Rho-independent termination Source: https:\u002F\u002Fwww.biolearners.com\n\n## Difference between transcription in prokaryotes and eukaryotes\n\n| Prokaryotic transcription | Eukaryotic transcription |\n| --- | --- |\n| Occurs in the cytoplasm | Occurs in the nucleus |\n| Only one RNA polymerase can synthesize all 3 types of RNA (mRNA, rRNA, tRNA ) | Three RNA polymerases, I, II, and III, synthesize rRNA, mRNA, and tRNA, respectively. |\n| Initiation of transcription does not need any initiation factors or proteins. | Initiation of transcription requires proteins called transcription factors ( TFIIA, TFIIB, TFIIID, TFIIE, TFIIF, and TFIIH) which recognize the TATA box. |\n| RNA polymerases are complexes of 5-polypeptides. | RNA polymerases are complexes of 10-15 polypeptides. |\n| Transcriptional unit has one or more genes (polycistronic) | Transcriptional unit has only one gene (monocistronic). |\n| Inhibitors: Rifampin: inhibits binding of RNA polymerase Actinomycin: interrupts the movement of RNA polymerase | Inhibitors: α-amanitin: inhibits RNA polymerase II. |\n\n**References:**\n\n- Madigan, M. T., Martinko, J. M., Stahl, D. A., & Clark, D. P. (2011). *BROCK Biology of Microorganisms* (13th edition). Benjamin Cumming.",[],[],[],[48,55,62,66,70,74,79,84,88,92],{"slug":49,"name":50,"description":51,"image":52,"body":53,"postCount":54},"acharya-tankeshwar","Acharya Tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",433,{"slug":56,"name":57,"description":58,"image":59,"body":60,"postCount":61},"ashma-shrestha","Ashma Shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",81,{"slug":63,"name":38,"description":64,"image":37,"body":37,"postCount":65},"sushmita-baniya","Author \u002F Contributor",32,{"slug":67,"name":68,"description":64,"image":37,"body":37,"postCount":69},"samikshya-acharya","Samikshya Acharya",20,{"slug":71,"name":72,"description":64,"image":37,"body":37,"postCount":73},"alisha-tripathi","Alisha Tripathi",6,{"slug":75,"name":76,"description":77,"image":37,"body":37,"postCount":78},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":80,"name":81,"description":82,"image":37,"body":37,"postCount":83},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":85,"name":86,"description":64,"image":37,"body":37,"postCount":87},"srijana-khanal","Srijana Khanal",18,{"slug":89,"name":90,"description":82,"image":37,"body":37,"postCount":91},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":93,"name":94,"description":64,"image":37,"body":95,"postCount":96},"nisha-rijal","Nisha Rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]