DiGIR2 is the group I splicing-ribozyme of themobile twin-ribozyme intron in Didymiumnuclear ribosomal DNA. DiGIR2 is responsible for intron excision, exon ligation,3¢-splice site hydrolysis,and full-length intron RNA circle formation. We recently reported that DiGIR2 splicing (intron excision and exon ligation) competes with hydrolysis and subsequent full-length intron circularization. Herewe present experimental evidence that hydrolysis at the 3¢-splice site in DiGIR2 is dependent on structural elements within the P9 subdomain not involved in splicing
