title: Convergent evolution of twintron-like configurations: One is never enough.
abstract: Introns inserted within introns are commonly referred to as twintrons, however the original definition for twintron implied that splicing of the external member of the twintron could only proceed upon splicing of the internal member. This review examines the various types of twintron-like arrangements that have been reported and assigns them to either nested or twintron categories that are subdivided further into subtypes based on differences of their mode of splicing. Twintron-like arrangements evolved independently by fortuitous events among different types of introns but once formed they offer opportunities for the evolution of new regulatory strategies and/or novel genetic elements.
authors.affiliation: a Department of Biochemistry ; Faculty of Medicine; University of Montreal ; Montréal , QC Canada.|b Department of Botany and Microbiology ; Faculty of Science; Suez University ; Suez , Egypt.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Hafez
authors.affiliation: c Department of Microbiology ; University of Manitoba ; Winnipeg , MB Canada.
authors.forename: Georg
authors.initials: G
authors.lastname: Hausner
mesh_terms: D019143:Evolution, Molecular; D007438:Introns / Q000235:genetics*; D009690:Nucleic Acid Conformation; D016337:RNA, Catalytic / Q000378:metabolism; D012343:RNA, Transfer / Q000235:genetics; D017381:Spliceosomes / Q000378:metabolism
chemical_list: D016337:RNA, Catalytic; D012343:RNA, Transfer
keywords: Twintrons; group I and II introns; intron shuffling; nested introns; ribozymes; spliceosome; tRNA introns