Figure 3

Model for intron-host interactions. The top half of the figure indicates that RNA chaperones and, sometimes, maturases and/or ribosomes are required to facilitate splicing of group I and group II introns, whereas replication, recombination and repair functions are necesary for homing of these elements in a host cell in a well balanced growth environment [80, 95]. Splicing of group II introns is, in turn, required for their mobility [15]. The bottom of the figure indicates how mobile introns respond to stress conditions in their host cell. For group I introns, oxidative stress results in group I endonuclease substrate infidelity, allowing transposition of the intron to sites with less sequence similarity than the normal allelic target [83]. For group II introns, nutritional stress increases their rate of transcription, thus raising the level of intron RNA, and also alters the disposition of the nucleoid (the bacterial DNA) in ways that favor retrotransposition; together these changes result in a burst of retrotransposition of group II introns in response to the stress [77].