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. 2021 Feb 1;10(2):290. doi: 10.3390/cells10020290

Figure 3.

Figure 3

RNPs of group II and spliceosomal introns. (A) The majority of bacterial group II introns form an RNP with the intron-encoded maturase during the splicing reactions [14]. (B) In organelles, group II introns are degenerated and RNPs comprise at least five splicing factors [20]. The maturase is either encoded by an organellar group II intron (matR, matK) sequence or is nucleus-encoded (nMat1–4; [28]). (C) Fragmented group II introns of C. reinhardtii depend on complex RNPs comprising up to ten splicing factors and the precursor RNAs. A maturase homolog has not been identified yet. (D) The five trans-acting snRNAs of the nuclear spliceosome probably originated from fragmentation of group II intron sequences. snRNAs associate with a large number of protein factors to form a complex with snRNPs and function in splicing of nuclear mRNA introns (reviewed in [4]). Homologies to group II intron maturases were shown for the splicing factor Prp8 [60]. Abbreviations: M, maturase; Mt, mitochondrial; cp, chloroplast.