An alternative intron-exon pairing scheme implied by unexpected in vitro activities of group II intron RmInt1 from Sinorhizobium meliloti.
RmInt1 is a mobile group II intron which interrupts ISRm2011-2, another mobile element from the bacterium Sinorhizobium meliloti. Ribozyme constructs derived from intron RmInt1 self-splice in vitro when incubated under permissive conditions, but the excised intron and ligated exons are largely replaced by unconventional products. These include a slightly shorter, 5'-end truncated 3' exon, truncated variants of the linear and lariat forms of the intron-3' exon reaction intermediate, as well as presumably circular molecules derived from the latter. Two factors explain the abundance of these products: (i) nucleotides 5-11 of the 3' exon (IBS1*) provide a better match to the EBS1 5'-exon-binding site than the authentic IBS1 sequence in the 5' exon; (ii) exon ligation is unusually inefficient, and especially so when the 5' exon is truncated close to the second (IBS2) intron-binding site. We propose that reactions at the IBS1* site play a part in the regulation of the intron ISRm2011-2 host in vivo.
Costa
María
M
Centre de Genétique Moléculaire du CNRS, Avenue de la Terrasse, 91190 Gif-sur-Yvette, France.
Michel
François
F
Molina-Sánchez
María Dolores
MD
Martinez-Abarca
Francisco
F
Toro
Nicolás
N
D017398:Alternative Splicing / Q000235:genetics*; D020029:Base Pairing / Q000235:genetics; D001483:Base Sequence; D005091:Exons / Q000235:genetics*; D007438:Introns / Q000235:genetics*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016337:RNA, Catalytic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016962:Sinorhizobium meliloti / Q000235:genetics*
D012329:RNA, Bacterial; D016337:RNA, Catalytic