Structure of the 5S rRNA genes in birch (Betula papyrifera) and alder (Alnus incana).

Hybridization of a 5S rDNA probe to Southern transfers of birch (Betula papyrifera) or alder (Alnus incana) DNA digested with BamH1 reveals similar triple-band "ladder-like" patterns. The sizes of sequenced 5S repeat units from both plants ranges only from 471 to 490 base pairs, suggesting that the complexity detected by Southern analysis is not due to different size classes of 5S repeats as found in other species. Within the intercistronic spacer region, conservation of large blocks of sequence between birch and alder 5S is observed implying a close evolutionary relationship between these two species. In both species, a duplication of part of the coding sequence including a restriction site for BamH1 introduces a second BamH1 site into the repeat unit. Differential methylation of the two BamHI restriction sites can account for the observed triple-band pattern.