A Member of the Mouse LRR Transcript Family with Homology to the Human Sp100 Gene

A previously isolated cDNA sequence with homology to the long‐range repeat (LRR) cluster in chromosome 1 of the house mouse, Mus musculus, was identified as derived from a 1.3 kb polyadenylated RNA. This transcript belongs to a family of polyadenylated RNAs which are synthesized from a multicopy gene included in the LRR copies.–‐The representation of the 1.3 kb transcript in genomic DNA was studied in X. and cosmid clones from the LRR cluster. Two different types of LRRs were detected with respect to the arrangement of coding regions. In the type‐1 arrangement, the sequence is split into five exons, and in the type‐2 arrangement, into six exons. The respective exons with their flanking regions were sequenced. The analysis of splice signals revealed that LRR copies with a type‐1 arrangement are presumably the source of the 1.3 kb transcript.–‐The 1.3 kb transcript has sequence homology to a human gene encoding Sp100, a nuclear antigen recognized by autoantibodies from patients suffering from some autoimmune diseases including primary biliary cirrhosis. Mouse exons II and III exhibit 71 % homology at the nucleotide level and 56 % homology at the amino acid level to the human Sp100 cDNA. We mapped the human SplOO gene to chromosome 2. This location corroborates the assumption that the human SplOO gene and the mouse LRR gene are homologous, as the human chromosome 2 contains the segment which is homologous to the mouse LRR region.