Genes for murine Y1 and Y3 Ro RNAs have class 3 RNA polymerase III promoter structures and are unlinked on mouse chromosome 6.

Murine YRNAs, which are components of the conserved Ro ribonucleoprotein (RNP) complex, have been identified by enzymatic RNA sequencing. Mouse Y1 (mY1) and Y3 (mY3; originally named mY2) RNAs share 97 and 95% identity to the human Y1 and Y3 RNAs, respectively. TATA-like sequences, Proximal Sequence Elements, and octamer sequences, which are upstream promoter element motifs indicative of Class 3 RNA Polymerase III (RNAPIII) transcribed genes, are found upstream of both the putative mY1 and mY3 coding regions. Further, these elements are strikingly conserved both in sequence and position relative to known Class 3 genes and to human YRNA genes. Inhibition of transcription in vitro by 200 micrograms/ml but not 1 microgram/ml of alpha-amanitin indicates transcription of the mouse YRNA genes by RNAPIII. Southern blot of C57BL/6J and Mus spretus murine genomic DNA with mY1 and mY3 gene-specific probes suggests that these genes are single copy in the mouse genome. Finally, gene mapping with a (C57BL/6J x SPRET/Ei)F1 x SPRET/Ei mouse interspecific backcross DNA panel localizes the mY1 gene to the distal end of mouse chromosome 6, close to the motheaten (me) autoimmunity locus. The mY3 gene maps to the proximal end of mouse chromosome 6 very close to the T cell receptor beta locus, in a region homologous to human chromosome 7 where the human YRNA genes have been mapped.