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In vivo expression of the nucleolar group I intron‐encoded I‐ Dir I homing endonuclease involves the removal of a spliceosomal intron
Author(s) -
Vader Anna,
Nielsen Henrik,
Johansen Steinar
Publication year - 1999
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/18.4.1003
Subject(s) - homing endonuclease , biology , intron , group ii intron , endonuclease , group i catalytic intron , genetics , rna splicing , homing (biology) , rna , gene , microbiology and biotechnology , ecology
The Didymium iridis DiSSU1 intron is located in the nuclear SSU rDNA and has an unusual twin‐ribozyme organization. One of the ribozymes (DiGIR2) catalyses intron excision and exon ligation. The other ribozyme (DiGIR1), which along with the endonuclease‐encoding I‐ Dir I open reading frame (ORF) is inserted in DiGIR2, carries out hydrolysis at internal processing sites (IPS1 and IPS2) located at its 3′ end. Examination of the in vivo expression of DiSSU1 shows that after excision, DiSSU1 is matured further into the I‐ Dir I mRNA by internal DiGIR1‐catalysed cleavage upstream of the ORF 5′ end, as well as truncation and polyadenylation downstream of the ORF 3′ end. A spliceosomal intron, the first to be reported within a group I intron and the rDNA, is removed before the I‐ Dir I mRNA associates with the polysomes. Taken together, our results imply that DiSSU1 uses a unique combination of intron‐supplied ribozyme activity and adaptation to the general RNA polymerase II pathway of mRNA expression to allow a protein to be produced from the RNA polymerase I‐transcribed rDNA.