Frequent site-specific mit- deletions at cryptic exon-intron junctions in the COX1 gene of yeast mtDNA.

A class of large site-specific deletions (del-B) occurs with exceptionally-high frequencies of 10(-3) in the mitochondrial COX1 gene of Mn(2+)-treated yeast cells. This work shows that del-B deletions are associated with COX1 intron aI1. All five deletion mutants studied have their upstream end at the authentic 3' splice site of this intron. The deletion ends 8.2 kb downstream in intron aI5b. This downstream deletion-end constitutes a potentially-cryptic 5' splice site for intron aI1. The coincidences of the del-B deletion-ends with authentic and cryptic RNA splice sites suggest that the group-II intron aI1, and/or the RNA maturase encoded in it, plays an active role in this exceptionally-frequent, site-specific deletion process.