An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term exon refers to both the DNA sequence within a gene and to the corresponding sequence in RNA transcripts. In RNA splicing, introns are removed and exons are covalently joined to one another as part of generating the mature RNA. Just as the entire set of genes for a species constitutes the genome, the entire set of exons constitutes the exome.
An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word intron is derived from the term intragenic region, i.e., a region inside a gene. The term intron refers to both the DNA sequence within a gene and the corresponding RNA sequence in RNA transcripts. The non-intron sequences that become joined by this RNA processing to form the mature RNA are called exons.
RNA splicing is a process in molecular biology where a newly-made precursor messenger RNA (pre-mRNA) transcript is transformed into a mature messenger RNA (mRNA). It works by removing all the introns and splicing back together exons. For nuclear-encoded genes, splicing occurs in the nucleus either during or immediately after transcription. For those eukaryotic genes that contain introns, splicing is usually needed to create an mRNA molecule that can be translated into protein. For many eukaryotic introns, splicing occurs in a series of reactions which are catalyzed by the spliceosome, a complex of small nuclear ribonucleoproteins (snRNPs). There exist self-splicing introns, that is, ribozymes that can catalyze their own excision from their parent RNA molecule. The process of transcription, splicing and translation is called gene expression, the central dogma of molecular biology.
Alternative splicing, or alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins. In this process, particular exons of a gene may be included within or excluded from the final, processed messenger RNA (mRNA) produced from that gene. This means the exons are joined in different combinations, leading to different (alternative) mRNA strands. Consequently, the proteins translated from alternatively spliced mRNAs usually contain differences in their amino acid sequence and, often, in their biological functions.
The Muroidea are a large superfamily of rodents, including mice, rats, voles, hamsters, lemmings, gerbils, and many other relatives. Although the Muroidea originated in Eurasia, they occupy a vast variety of habitats on every continent except Antarctica. Some authorities have placed all members of this group into a single family, Muridae, due to difficulties in determining how the subfamilies are related to one another. Many of the families within the Muroidea superfamily have more variations between the families than between the different clades. A possible explanation for the variations in rodents is because of the location of these rodents; these changes could have been due to radiation or the overall environment they migrated to or originated in. The following taxonomy is based on recent well-supported molecular phylogenies.
Exon shuffling is a molecular mechanism for the formation of new genes. It is a process through which two or more exons from different genes can be brought together ectopically, or the same exon can be duplicated, to create a new exon-intron structure. There are different mechanisms through which exon shuffling occurs: transposon mediated exon shuffling, crossover during sexual recombination of parental genomes and illegitimate recombination.
Growth hormone receptor is a protein that in humans is encoded by the GHR gene. GHR orthologs have been identified in most mammals.
Vitamin A receptor, Stimulated by retinoic acid 6 or STRA6 protein was originally discovered as a transmembrane cell-surface receptor for retinol-binding protein. STRA6 is unique as it functions both as a membrane transporter and a cell surface receptor, particularly as a cytokine receptor. In fact, STRA6 may be the first of a whole new class of proteins that might be known as "cytokine signaling transporters." STRA6 is primarily known as the receptor for retinol binding protein and for its relevance in the transport of retinol to specific sites such as the eye. It does this through the removal of retinol (ROH) from the holo-Retinol Binding Protein (RBP) and transports it into the cell to be metabolized into retinoids and/or kept as a retinylester. As a receptor, after holo-RBP is bound, STRA6 activates the JAK/STAT pathway, resulting in the activation of transcription factor, STAT5. These two functions—retinol transporter and cytokine receptor—while using different pathways, are processes that depend on each other.
In evolutionary biology, the flying primate hypothesis is that megabats, a subgroup of Chiroptera, form an evolutionary sister group of primates. The hypothesis began with Carl Linnaeus in 1758, and was again advanced by J.D. Smith in 1980. It was proposed in its modern form by Australian neuroscientist Jack Pettigrew in 1986 after he discovered that the connections between the retina and the superior colliculus in the megabat Pteropus were organized in the same way found in primates, and purportedly different from all other mammals. This was followed up by a longer study published in 1989, in which this was supported by the analysis of many other brain and body characteristics. Pettigrew suggested that flying foxes, colugos, and primates were all descendants of the same group of early arboreal mammals. The megabat flight and the colugo gliding could be both seen as locomotory adaptations to a life high above the ground.
IRBP may refer to two proteins:
RPE-retinal G protein-coupled receptor also known as RGR-opsin is a protein that in humans is encoded by the RGR gene. RGR-opsin is a member of the rhodopsin-like receptor subfamily of GPCR. Like other opsins which bind retinaldehyde, it contains a conserved lysine residue in the seventh transmembrane domain. RGR-opsin comes in different isoforms produced by alternative splicing.
ATP-binding cassette, sub-family A (ABC1), member 4, also known as ABCA4 or ABCR, is a protein which in humans is encoded by the ABCA4 gene.
Retinal pigment epithelium-specific 65 kDa protein, also known as retinoid isomerohydrolase, is an enzyme of the vertebrate visual cycle that is encoded in humans by the RPE65 gene. RPE65 is expressed in the retinal pigment epithelium and is responsible for the conversion of all-trans-retinyl esters to 11-cis-retinol during phototransduction. 11-cis-retinol is then used in visual pigment regeneration in photoreceptor cells. RPE65 belongs to the carotenoid oxygenase family of enzymes.
Retinaldehyde-binding protein 1 (RLBP1) also known as cellular retinaldehyde-binding protein (CRALBP) is a 36-kD water-soluble protein that in humans is encoded by the RLBP1 gene.
Retinol binding protein 1, cellular, also known as RBP1, is a protein that in humans is encoded by the RBP1 gene.
Homeobox protein OTX2 is a protein that in humans is encoded by the OTX2 gene.
Retinol-binding protein 2 (RBP2) is a protein that in humans is encoded by the RBP2 gene.
Retinol dehydrogenase 12 is an enzyme that in humans is encoded by the RDH12 gene.
Retinol-binding proteins (RBP) are a family of proteins with diverse functions. They are carrier proteins that bind retinol. Assessment of retinol-binding protein is used to determine visceral protein mass in health-related nutritional studies.
The split gene theory is a theory of the origin of introns, long non-coding sequences in eukaryotic genes between the exons. The theory holds that the randomness of primordial DNA sequences would only permit small (< 600bp) open reading frames (ORFs), and that important intron structures and regulatory sequences are derived from stop codons. In this introns-first framework, the spliceosomal machinery and the nucleus evolved due to the necessity to join these ORFs into larger proteins, and that intronless bacterial genes are less ancestral than the split eukaryotic genes. The theory originated with Periannan Senapathy.
