N. Loizos et al., EVOLUTION OF MOBILE GROUP-I INTRONS - RECOGNITION OF INTRON SEQUENCESBY AN INTRON-ENCODED ENDONUCLEASE, Proceedings of the National Academy of Sciences of the United Statesof America, 91(25), 1994, pp. 11983-11987
Mobile group I introns are hypothesized to have arisen after invasion
by endonuclease-encoding open reading frames (ORFs), which mediate the
ir mobility, Consistent with an endonuclease-ORF invasion event, we re
port similarity between exon junction sequences (the recognition site
for the mobility endonuclease) and intron sequences flanking the endon
uclease ORF in the sunY gene of phage T4, Furthermore, we have demonst
rated the ability of the intron-encoded endonuclease to recognize and
cleave these intron sequences when present in fused form in synthetic
constructs. These observations and accompanying splicing data are cons
istent with models in which the invading endonuclease ORF is provided
safe haven within a splicing element. In turn the intron is afforded i
mmunity to the endonuclease product, which imparts mobility to the int
ron.