Cloning and characterization of rat 4.5S RNAj genes

Genomic clones containing genes for 4.5S RNA., which is an abundant small nuclear RNA found in rodent cells, were obtained from a rat genomic library. Thirty-four clones that formed RNase A resistant hybrids with 3'-end-labeled 4.5S RNAT were isolated, and seven of them (clones XI39, XI41, XI42, XI51, XI106, XI123 and XI154) were characterized by sequencing and j_n vitro transcription. Clones XI41 and XI123 carry one and two genes, respectively, with identical sequences to that of 4.5S RNA, and are actively transcribed j_n vitro. However, the other five clones contain sequences that seem to be pseudogenes for 4.5S RNA., since they have nucleotide substitutions or deletions in the sequence corresponding to 4.5S RNA. or are not transcribed. Four clones (XI39, XI42, XI106 and XI154) were found to have 13-18 nucleotide-long direct repeats flanking the 4.5S RNA. sequences. The genomic organization of the genes and their related sequences is discussed