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Related Concept Videos

Leaky Scanning02:28

Leaky Scanning

During most eukaryotic translation processes, the small 40S ribosome subunit scans an mRNA from its 5' end until it encounters the first start AUG codon. The large 60S ribosomal subunit then joins the smaller one to initiate protein synthesis. The location of the translation initiation is largely determined by the nucleotides near the start codon as there may be multiple translation initiation sites present on the mRNA.  Marilyn Kozak discovered that the sequence RCCAUGG (where R stands for...
Ribosome Profiling02:24

Ribosome Profiling

Ribosome profiling or ribo-sequencing is a deep sequencing technique that produces a snapshot of active translation in a cell. It selectively sequences the mRNAs protected by ribosomes to get an insight into a cell’s translation landscape at any given point in time.
Applications of ribosome profiling
Ribosome profiling has many applications, including in vivo monitoring of translation inside a particular organ or tissue type and quantifying new protein synthesis levels.
The technique helps...
Initiation of Translation02:33

Initiation of Translation

Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at...
pre-mRNA Processing02:01

pre-mRNA Processing

In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or pre-mRNA to distinguish it from mature mRNA.
Once about 20-40 ribonucleotides have been joined together by RNA polymerase, a group of enzymes adds a “cap” to the 5’ end of the growing transcript. In this process, a 5’ phosphate is replaced by modified guanosine that has a methyl group attached to it (7-Methyl guanosine). This 5’ cap helps the...
Regulation of Expression Occurs at Multiple Steps02:24

Regulation of Expression Occurs at Multiple Steps

Gene expression can be regulated at almost every step from gene to protein. Transcription is the step that is most commonly regulated. This involves the binding of proteins to short regulatory sequences on the DNA. This association can either promote or inhibit the transcription of a gene associated with the respective sequence.
Transcription results in the generation of precursor (pre-mRNA) that consists of both exons and introns, which needs further processing before being translated to a...
Eukaryotic RNA Polymerases00:58

Eukaryotic RNA Polymerases

RNA Polymerase (RNAP) is conserved in all animals, with bacterial, archaeal, and eukaryotic RNAPs sharing significant sequence, structural, and functional similarities. Among the three eukaryotic RNAPs, RNA Polymerase II is most similar to bacterial RNAP in terms of both structural organization and folding topologies of the enzyme subunits. However, these similarities are not reflected in their mechanism of action.
All three eukaryotic RNAPs require specific transcription factors, of which the...

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Related Experiment Video

Updated: Jun 19, 2026

Polysome Fractionation and Analysis of Mammalian Translatomes on a Genome-wide Scale
10:56

Polysome Fractionation and Analysis of Mammalian Translatomes on a Genome-wide Scale

Published on: May 17, 2014

New insights into polycistronic transcripts in eukaryotes.

Haiwei Pi1, Li-Wei Lee, Szecheng J Lo

  • 1Department of Life Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.

Chang Gung Medical Journal
|October 21, 2009
PubMed
Summary
This summary is machine-generated.

Polycistronic transcripts, previously rare in eukaryotes, are now found in insects, challenging prior assumptions. These transcripts allow simultaneous translation of multiple genes, including small peptides, offering new evolutionary insights.

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Polysome Profiling in Leishmania, Human Cells and Mouse Testis

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Related Experiment Videos

Last Updated: Jun 19, 2026

Polysome Fractionation and Analysis of Mammalian Translatomes on a Genome-wide Scale
10:56

Polysome Fractionation and Analysis of Mammalian Translatomes on a Genome-wide Scale

Published on: May 17, 2014

In vivo Interrogation of Central Nervous System Translatome by Polyribosome Fractionation
09:13

In vivo Interrogation of Central Nervous System Translatome by Polyribosome Fractionation

Published on: April 30, 2014

Polysome Profiling in Leishmania, Human Cells and Mouse Testis
14:32

Polysome Profiling in Leishmania, Human Cells and Mouse Testis

Published on: April 8, 2018

Area of Science:

  • Genomics
  • Molecular Biology
  • Evolutionary Biology

Background:

  • Functionally related genes in bacteria and archaea are organized into operons for simultaneous transcription and translation.
  • Operons are generally absent in eukaryotes, with exceptions like Trypanosoma and nematodes where transcripts are processed into individual mRNAs.

Purpose of the Study:

  • To investigate the presence and implications of polycistronic transcripts in eukaryotes, specifically insects.
  • To re-evaluate the understanding of gene organization and evolution in eukaryotes.

Main Methods:

  • Analysis of recently identified polycistronic transcripts in insects.
  • Comparative genomics and transcriptomics approaches (details not specified in abstract).

Main Results:

  • Polycistronic transcripts, similar to prokaryotic operons, have been identified in insects.
  • These transcripts enable simultaneous translation of encoded peptides or proteins from a single mRNA.
  • Newly discovered polycistronic genes encode biologically significant small peptides (as short as 11 amino acids).

Conclusions:

  • The findings revise the understanding of eukaryotic gene organization, indicating polycistronic genes are not as rare as previously thought.
  • The discovery of small peptide-encoding polycistronic genes necessitates a redefinition of coding sequences in genomic annotation.
  • This opens avenues for identifying more small peptides in genome-solved organisms and understanding their evolutionary significance.