“…The minimal number of gRNAs required for productive editing of a pre-edited mRNA is determined by the number of editing blocks+ In the UC strain of L. tarentolae, there are 15 gRNAs encoded in the maxicircle DNA and a total of 17 gRNAs encoded in the approximately 10,000 catenated minicircle molecules that comprise the kinetoplast DNA network (Maslov & Simpson, 1992)+ The copy numbers of the different minicircle sequence classes exhibit a large variability and show a rapid rate of change in laboratory cultures (Simpson et al+, 2000)+ Five pan-edited cryptogenes in the UC strain that were labeled G1-G5 are not productively edited due to the absence of the required gRNAs, and the proteins are not expressed, indicating that these proteins are not required for life in culture (Thiemann et al+, 1994)+ However, transcripts of the homologous cryptogenes in the related species Trypanosoma brucei are productively edited in both stages of the biphasic life cycle, and the identified products include ND8, ND9, and ND3 (Read et al+, 1992(Read et al+, , 1994Souza et al+, 1992Souza et al+, , 1993Corell et al+, 1994)+ We showed previously that in the recently isolated LEM125 strain of L. tarentolae, the transcripts of these cryptogenes are also productively edited, which implies the presence of overlapping cascades of specific gRNAs in that strain (Thiemann et al+, 1994)+ In the initial work, 32 new gRNAs were identified from gRNA and minicircle DNA libraries, but it was estimated that at least 80 gRNAs would be required for the complete editing of these five cryptogene transcripts (Thiemann et al+, 1994)+ In this article, we have detected an additional 20 minicircle-encoded gRNAs that cover almost all the remaining blocks of editing in the transcripts of ND8, ND9, ND3, G4, and G5 from the LEM125 strain of L. tarentolae+ We have also discovered 18 pairs of redundant gRNAs, which are gRNAs of different sequences that could edit the same mRNA sequence block and are the result of the allowance of G:U as well as the canonical G:C base pairing in the gRNA:mRNA interaction+ No redundant gRNAs were previously seen in the UC strain (Maslov & Simpson, 1992) and only a single pair of redundant gRNAs was found in the initial study of the LEM125 strain (Thiemann et al+, 1994)+ The evolutionary implications of this evidence are discussed+…”