S. Johansen et al., IN-VIVO MOBILITY OF A GROUP-I TWINTRON IN NUCLEAR RIBOSOMAL DNA OF THE MYXOMYCETE DIDYMIUM-IRIDIS, Molecular microbiology, 24(4), 1997, pp. 737-745
DiSSU1 is an optional group I twintron present in the nuclear extrachr
omosomal ribosomal DNA of the myxomycete Didymium iridis, DISSU1 appea
rs to be complex both in structure and function. At the RNA level it h
as a twin-ribozyme organization composed of two group I ribozymes with
different functions, separated by an open reading frame. Here, we sho
w that DISSU1 is mobile when haploid intron-containing and intron-less
amoebae are mated, The mobility process is fast, being completed in 5
-10 nuclear cycles after mating in the developing zygote and plasmodia
, Analyses of progeny from genetic crosses confirm intron mobility, Di
SSU1 is the first example of a mobile group I twintron, The intron-enc
oded protein was expressed in Escherichia coil and found to be an endo
nuclease, I-Dirl, that cleaves an intron-less ribosomal DNA allele at
the intron-insertion site, and is probably involved in intron homing,
The endonuclease I-Dirl seems to be a rare example of a protein that i
s expressed from a ribozyme-processed RNA polymerase I transcript in v
ivo.