FUGU INTRON OVERSIZE REVEALS THE PRESENCE OF U15 SNORNA CODING SEQUENCES IN SOME INTRONS OF THE RIBOSOMAL-PROTEIN S3 GENE

We present here the analysis of the genomic organization of the Fugu g ene coding for ribosomal protein S3 and its intron encoded U15 RNA, an d compare it with the homologous human and Xenopus genes. Only two of the six Fugu S3 gene introns do not contain the U15 sequence and are i n fact shorter than 100 nucleotides, as most Fugu introns. The other f our introns are somewhat longer and contain sequences homologous to U1 5 RNA; two of these represent functional copies, as shown by microinje ctions of Fugu transcripts into Xenopus oocytes, whereas the other two appear to be nonfunctional pseudocopies. Thus Fugu turns out to be id eal for the study of intron encoded snoRNAs, partly because of the red uced cloning and sequencing workload, and partly because the intron le ngth per se can be an indication of the presence of a snoRNA coding se quence.