This is the insertion site of the mobile intron that angiosperms acquired on multiple occasions [ 41].
Finally, with respect to the probability of intron gain, the cox1 intron is so clearly a highly mobile intron that to postulate one additional horizontal transfer (two gains within Solanoideae rather than one), when more than 80 such events have already been documented [ 8- 12], hardly stretches the bounds of imagination.
RmInt1 is a mobile group II intron that is widespread in natural populations of Sinorhizobium meliloti and was first described in the GR4 strain.
RmInt1 is a mobile bacterial group II intron that is widespread in natural populations of S. meliloti (Muñoz et al., 2001) and was first described in the GR4 strain (Martínez-Abarca et al., 1998).
Although each intron that was similar in size in pb-1 was slightly larger than the corresponding intron in pb-3, each type of intron was in the same order in pb-1 and pb-3.
Homing endonucleases are highly specific DNA endonucleases, encoded within mobile introns or inteins, that induce targeted recombination, double-strand repair and gene conversion of their cognate target sites.
These observations suggest that the single mobile intron in the Floydiella chloroplast is of recent origin and was acquired through lateral transfer of a mobile intron from a mitochondrial genome donor.
We have examined the gain and loss of the HEG only among the intron-containing strains, since no existing theories suggest a high frequency of gains and losses of the HEG within the ω intron, and the turnover rate of HEG within the intron would be expected to be very low compared with that of the mobile intron based on the intron-homing model.
Our conclusions on a mitochondrial group I intron in this study could have a broad implication that gene conversion within a mobile intron can alter the presence/absence and the function of an endonuclease or a retrotranscriptase and ultimately promote the gain and loss of the mobile intron.
Also surprising is our finding that the LAGLIDADG endonuclease specified by this unique mobile intron displays sequence similarity with proteins encoded by introns in the mitochondrial rnl, cox1, and atp6 genes of the fungi Smittium culisetae (E value = 3 × 10−12), Giberella zeae (E value = 5 × 10−11), and Neurospora crassa (E value = 9 × 10−9), respectively.
It is tempting to speculate that mobile introns were once present in the common ancestor of the Chaetopeltidales and that the homing endonuclease genes conferring their mobility were extinguished because of their role in amplifying noncoding DNA through intron transpositions and constraints to eliminate excessive noncoding DNA in the Floydiella lineage.
