Complementary deletions in expressed potato U2snRNA gene variants support the hypothesis that stem—loop IIb is dispensable for splicing

A polymerase chain reaction (PCR) strategy designed to amplify DNA sequences between closely linked U2snRNA genes has generated extensive coding and 5′ regulatory sequence information on the potato U2snRNA multigene family. Two of the U2snRNA coding sequences isolated differed substantially from normal U2snRNAs by containing both complementary deletions and regions of novel sequence. However, sequences such as Sm‐binding sites and loops of stem—loops III and IV, which are some of the most highly conserved regions in U2snRNA, remain highly conserved in these genes. The complementary deletions would effectively remove stem—loop IIb which has been shown in yeast to be unnecessary for pre‐mRNA splicing. Transcripts from one of the genes have been detected by reverse transcriptase‐PCR (RT‐PCR) in total RNA. These novel U2snRNA genes represent the first reported example of naturally occurring structural variants and provide support for the proposed non‐essential role of U2snRNA stem—loop IIb.