The owners of a local bakery ask for your help in improving a special yeast strain they use to make bread

Question

They would like you to help them design experiments using RNA interference to turn off genes, to allow them to test their hypothesis that certain genes are important for the good flavors found in their bread. Of the components in the following list, which is the most important to check for in this yeast strain if you'd like this project to succeed?
(a) the presence of foreign double-stranded RNA
(b) the presence of genes in the genome that code for RISC proteins
(c) the presence of miRNA genes in the genome
(d) the presence of single-stranded siRNAs within the cell

Answer 1

(b) Without RISC proteins, the RNA degradation necessary to turn off genes would not occur. Foreign double-stranded RNA induces RNAi and cells with an intact RNAi response would not be expected to have foreign double-stranded RNA stably present [choice (a)]. miRNA genes could be present in the genome of cells without an intact RNAi response if the ancestral cell did have RNAi capabilities that were lost though evolutionary time [choice (c)]. Although the presence of single-stranded siRNAs within the cell may indicate the presence of Dicer, Dicer alone cannot carry out RNAi without RISC. In fact, if Dicer were absent but RISC present, it may still be possible to carry out RNAi by providing the cell with short, 23-nucleotide-pair siRNAs [choice (d)].