Lactis-leu-phe leader RNA motif
Encyclopedia
The leu/phe-leader RNA motif (also the lactis-leu/phe-leader motif) is a conserved RNA
structure identified by bioinformatics
. These RNAs function as peptide leaders
. They contain a short open reading frame
(ORF) that contains many codons for leucine
or phenylalanine
. Normally, expression of the downstream gene
s is suppressed. However, when cellular concentrations of the relevant amino acid
is low, ribosome
stalling leads to an alternate structure that enables downstream gene expression.
Leu/phe leaders of this structure are known only in the species Lactococcus lactis
, and is essentially the same as a previously characterized leucine
leader in the same species. Additional homologs
were uncovered that contain phenylalanine codons instead of leucine codons, and are upstream of genes involved in the synthesis of phenylalanine, instead of leucine.
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
structure identified by bioinformatics
Bioinformatics
Bioinformatics is the application of computer science and information technology to the field of biology and medicine. Bioinformatics deals with algorithms, databases and information systems, web technologies, artificial intelligence and soft computing, information and computation theory, software...
. These RNAs function as peptide leaders
Attenuator (genetics)
Attenuation is a regulatory feature found throughout Archaea and Bacteria causing premature termination of transcription. Attenuators are 5'-cis acting regulatory regions which fold into one of two alternative RNA structures which determine the success of transcription...
. They contain a short open reading frame
Open reading frame
In molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...
(ORF) that contains many codons for leucine
Leucine
Leucine is a branched-chain α-amino acid with the chemical formula HO2CCHCH2CH2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins...
or phenylalanine
Phenylalanine
Phenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form...
. Normally, expression of the downstream gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s is suppressed. However, when cellular concentrations of the relevant amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
is low, ribosome
Ribosome
A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
stalling leads to an alternate structure that enables downstream gene expression.
Leu/phe leaders of this structure are known only in the species Lactococcus lactis
Lactococcus lactis
Lactococcus lactis is a Gram-positive bacterium used extensively in the production of buttermilk and cheese, but has recently also become famous as the first genetically modified organism to be used alive for the treatment of human disease. L...
, and is essentially the same as a previously characterized leucine
Leucine
Leucine is a branched-chain α-amino acid with the chemical formula HO2CCHCH2CH2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins...
leader in the same species. Additional homologs
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
were uncovered that contain phenylalanine codons instead of leucine codons, and are upstream of genes involved in the synthesis of phenylalanine, instead of leucine.