A ribosomal protein leader is a mechanism used in
cells
Cell most often refers to:
* Cell (biology), the functional basic unit of life
* Cellphone, a phone connected to a cellular network
* Clandestine cell, a penetration-resistant form of a secret or outlawed organization
* Electrochemical cell, a d ...
to control the cellular concentration of a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
that forms a part of the
ribosome
Ribosomes () are molecular machine, macromolecular machines, found within all cell (biology), cells, that perform Translation (biology), biological protein synthesis (messenger RNA translation). Ribosomes link amino acids together in the order s ...
, and to make sure that the concentration is neither too high nor too low.
Ribosomal protein leaders are
RNA
Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...
sequences that are a part of the
5' UTR
The 5′ untranslated region (also known as 5′ UTR, leader sequence, transcript leader, or leader RNA) is the region of a messenger RNA (mRNA) that is directly Upstream and downstream (DNA), upstream from the initiation codon. This region is im ...
of
mRNA
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein.
mRNA is ...
s encoding a ribosomal protein. When cellular concentrations of the ribosomal protein are high, excess protein will bind to the mRNA leader. This binding event can lower gene expression via a number of mechanisms; for example, in the protein-bound state, the RNA could form an
intrinsic transcription termination stem-loop
Stem-loops are nucleic acid Biomolecular structure, secondary structural elements which form via intramolecular base pairing in single-stranded DNA or RNA. They are also referred to as hairpins or hairpin loops. A stem-loop occurs when two regi ...
. When cellular concentrations of the ribosomal protein are not high, they are occupied in the ribosome, and are not available in significant quantities to bind the mRNA leader. This leads to increased expression of the gene, which leads to the synthesis of more copies of the ribosomal protein. Many examples of ribosomal protein leaders are known in
bacteria
Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
, including
ribosomal protein L20 leader and
ribosomal S15 leader
S15 Ribosomal protein leaders perform an important regulatory function in ribosome biogenesis. They were used as an autoregulatory mechanism to control the concentration of ribosomal proteins S15. The structure is located in the 5′ untranslated ...
.
Ribosomal leaders typically bind
ribosomal protein
A ribosomal protein (r-protein or rProtein) is any of the proteins that, in conjunction with rRNA, make up the ribosomal subunits involved in the cellular process of translation. ''E. coli'', other bacteria and Archaea have a 30S small subunit ...
s that normally bind
ribosomal RNA
Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...
. In many cases, the binding site within the leader structurally resembles the region of the ribosomal RNA to which the protein binds, in an example of molecular mimicry.
See also
:
References
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