[Nucleotide sequence of the repetitive B2 region of the mouse genome]

Mouse genome contains two major families of short interspersed repeats in more than 10(5) copies and scattered throughout the whole genome. They were named as B1 and B2 sequences since they were first isolated from the genome library by means of a dsRNA-B probe. Three copies of B2 family were sequenced and compared with previously sequenced B1 repeat. B2 ubiquitous repeat is of ca. 180 bp long. The members of the family deviate by 5% of nucleotides from the consensus sequence. B2 contains the regions of homology to RNA polymerase III split promoter and to 4.5 S snRNA I. In contrast to B1, it does not contain clear homologies to exon-intron junctions, papova replication origins and human Alu-sequence. One side of B2 repeat is represented by a very AT-rich sequence (30 bp long) followed with an oligo(A) stretch 10-15 nucleotides long. This region of the repeat is the most variable one. The unit is flanked by 15-16 bp direct repeats different in sequenced copies of B2. The same is true for some copies of B1 family. The properties of B1 and B2 repeats suggest that they represent a novel class of transposon-like elements of eukaryotic genome. The possible role of B-type repeats in genome reorganization, DNA replication and pre-mRNA processing is discussed.