The catalytic core of the sunY intron of bacteriophage T4.

The self-splicing sunY intron of bacteriophage T4 shares a common secondary structure with other group I introns. A long open reading frame within the intron is entirely 3' of the structural elements conserved in all group I introns. This catalytic core is the smallest yet described for a self-splicing intron. An internal deletion of 728 nucleotides (nt), leaving 196 nt at the 5' end and 109 nt at the 3' end, allows normal self-splicing. Transcripts terminating 196 nt 3' of the 5' splice site retain catalytic activity.