RODENT BC1 RNA GENE AS A MASTER GENE FOR ID ELEMENT AMPLIFICATION

ID elements are short interspersed repetitive DNA elements (SINEs) whi ch have amplified in rodent genomes via retroposition, a process invol ving an RNA intermediate. BC1, an abundant ID-related transcript, is t ranscribed from a conserved, single-copy gene in rodents. The gene enc oding BC1 RNA represents one of the earliest and possibly the first ID -containing sequence. Comparison of consensus sequences of each rodent ID with its corresponding BC1 RNA gene showed that the variations of BC1 RNA within rodents corresponded to specific changes within the ID consensus sequence for each rodent species. This supports the hypothes is that the BC1 gene is a master gene responsible for the amplificatio n and evolution of ID elements. The rat ID family consists of at least four subfamilies, with the oldest subfamily having been derived from the BC1 RNA. The other three subfamilies appear to have been derived f rom a new master gene(s), which has been responsible for the large inc rease in ID element copy number within the rat genome. We have found t hat the guinea pig genome contains two copies of the BC1 gene, apparen tly the result of a DNA-mediated duplication event. Both of these guin ea pig BC1 genes have a conserved TATA-like element in the 5' flanking region and have contributed to guinea pig ID amplifications.