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 seq uences between closely linked U2snRNA genes has generated extensive co ding and 5' regulatory sequence information on the potato U2snRNA mult igene family. Two of the U2snRNA coding sequences isolated differed su bstantially from normal U2snRNAs by containing both complementary dele tions and regions of novel sequence. However, sequences such as Sm-bin ding sites and loops of stem-loops III and IV, which are some of the m ost highly conserved regions in U2snRNA, remain highly conserved in th ese genes. The complementary deletions would effectively remove stem-l oop IIb which has been shown in yeast to be unnecessary for pre-mRNA s plicing. Transcripts from one of the genes have been detected by rever se 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 U 2snRNA stem-loop IIb.