Protein splicing
Oxford Dictionary of Genetics:
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Protein Splicing
a phenomenon (known to occur in yeast, bacteria, and archaeons) during which a precursor protein has a segment excised from it and the N- and C-terminal fragments are subsequently spliced together. The excised segment is called an intein (internal protein sequence), and the spliced protein is composed of N- and C-exteins (external protein sequence). An intein cuts itself from its parent molecule and unites its former neighboring exteins with the usual peptide bond. Introns (q.v.) often encode a “homing endonuclease” (q.v.) that can excise a DNA segment, allowing it to move to a new genomic location. Analogously, many inteins contain a “homing endonuclease” segment in addition to a protein splicing region. This kind of intein can excise the DNA that encodes it out of a gene and allow the DNA to be transported elsewhere. A DNA polymerase in Synechocystis (q.v.) is encoded by two gene segments sandwiched between several other genes. Each segment terminates in half of an intein gene (a “split intein”). When their protein products make contact, the intein reassembles itself and splices the two polymerase segments together. Compare withfused protein, fusion gene. See Chronology, 1990, Kane et al.; 1997, Klenk et al.; posttranslational processing.
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Protein splicing
Protein splicing is an intramolecular reaction of a particular protein in which an internal protein segment (called an intein) is removed from a precursor protein with a ligation of C-terminal and N-terminal external proteins (called exteins) on both sides. The splicing junction of the precursor protein is mainly a cysteine or a serine, which are amino acids containing a nucleophilic side chain. The protein splicing reactions which are known now do not require exogenous cofactors or energy sources such as adenosine triphosphate (ATP) or guanosine triphosphate (GTP). Normally, splicing is associated only with pre-mRNA splicing.
Types of inteins
The type of the splicing proteins is categorized into four classes: maxi-intein, mini-intein, trans-splicing intein, and alanine intein. The maxi-inteins are N- and C-terminal splicing domains containing an endonuclease domain. The mini-inteins are typical N- and C-terminal splicing domains; however, the endonuclease domain is not present. The trans-splicing inteins are split inteins which are divided into N-termini and C-termini. Alanine inteins have the splicing junction of an alanine instead of a cysteine or a serine, in both of which the protein splicing occurs.
History
Protein splicing was reported by two groups (Anraku and Stevens) in 1990. They both discovered a Saccharomyces cerevisiae VMA1 in a precursor of a vacuolar H+-ATPase. The amino acid sequence of the N- and C-termini corresponded to 70% of that of a vacuolar H+-ATPase from other organisms, while the amino acid sequence of the central position corresponded to 30% of that of the yeast HO nuclease
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Oxford Dictionary of Genetics
A Dictionary of Genetics. © 2006
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