The rabbit C family of short, interspersed repeats

The C repeat family was first observed in the rabbit β-like globin gene family. We have estimated the repetition frequency of the C repeats, determined the nucleotide sequence of three intact members and one truncated member, and have investigated the size, tissue specificity, and intracellular localization of C repeat transcripts. Members of the C repeat family are short (average size of 316 basepairs) and are repeated about 170,000 times per haploid genome in a widely dispersed pattern. They end in a 3′ poly(dA) tract and are flanked by direct repeats that range in size from 8 to 16 base-pairs. The consensus internal control regions for polymerase III transcription are located near the 5′ end. Different amounts of C repeat RNA accumulate in a variety of tissues, and most of the transcripts are confined to the nucleus. A heterogeneous distribution of C repeat RNA sizes was found, ranging from about 330 to 8200 nucleotides. These structural and transcriptional properties are similar to those of primate and rodent Alu and Alu -like repeats. However, the C repeats are not similar in sequence to the Alu repeats. Thus two different types of short, interspersed repeats capable of being transcribed and proposed to be transposable elements have now been identified in mammals. The positions of these short repeats in mammalian β-like globin gene families are not tightly conserved.