Yeast U6 snRNA made by RNA polymerase II is less stable but functional

Creation of a consensus Sm-binding site in U6-II increases its stability. (A) Substitutions (in red) introduced in U6-II to replace its 3′ end with that of U4 snRNA, including the Sm-binding site (A₂U₅G₂). Replacement of 6 nt of U6 with nine of U4 elongate U6-II-Sm by 3 nt. (B) Total RNA was extracted from cells with WT U6, U6-II, or U6-II-Sm collected at the indicated times after transfer from YEP-galactose to YEP-glucose. The RNA was subjected to primer extension to detect U1, U4, and U6 snRNAs as well as unspliced and spliced U3 snoRNA. (Note that a different U6 primer, U6B, was used than in Fig. 3.) (C) Quantitation of U6, U4, and mature U3 RNA present in the gel from part B relative to the WT strain immediately before shift from galactose to glucose (0 h). (D) Quantitation of pre-U3 snoRNA present in the gel from part B relative to the WT strain immediately before shift from galactose to glucose (0 h). Values are normalized to U1 snRNA in each sample to control for variable RNA recovery.