Bacteriophage introns

Although spliceosomal introns appear to be limited to eukaryotes, the other intron classes are not. Genes with group I and II introns have now been found in both bacteria and bacterial viruses. Bacteriophage T4, for example, has several protein-encoding genes with group I introns. Introns appear to be more common in archae-bacteria than in eubacteria. 

RNAs produced in vitro are useful in the development of in vitro splicing systems where the RNA produced is a primary transcript. In addition, the RNA can be used as a template for in vitro translation, and in mapping exons tuid introns in genomic DNA. Genes under control of bacteriophage promoters can also be expressed in bacterial cells to facilitate expression and/or purification of the proteins they encode. 

Class I introns were originally discovered in ciliated protozoa and subsequently were found in fungi, bacteriophages, and other organisms. The RNA itself in a class I in-tron has catalytic activity and class I introns remove themselves from primary RNA transcripts by a self-splicing reaction. Class I introns are not true enzymes in that they function only once. The nucleotides in the intron that is spliced out are recycled in the cell. 

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