Conserved sequence patterns in the non-coding ribosomal ITS-1 of distantly related snail taxa

摘要

The ensuing contribution gives an insight into the evolution of non-coding ribosomal DNA of two distantly related groups of snails. The non-coding sequences of the ribosomal DNA comprise the First Internal Transcribed Spacer (ITS-1), the Second Internal Transcribed Spacer (ITS-2), and the Non-Transcribed Spacer (NTS). These spacers are known to evolve faster than the coding 18S, 5.8S and 28S ribosomal DNA~(1,2,3). The fast evolution of the spacers can be used to investigate the genetic relationships of closely related genera, species and other lower taxonomic units with a divergence time of less than 50 million years~(3,4,5). The focus of our analysis is on the evolution of the ITS-1 of land snails (Stylommatophora) and of freshwater snails (Basommatophora). These two snail groups have their origin in the Mesozoic. Consequently, we expected their ITS-1 sequences to show strong differences. However, the ITS-1 of stylommatophoran and basommatophoran gastropods is consecutively divided into conserved and variable regions. The detection of conserved ITS-1 regions among distantly related animals gives further insight into the functional significance of non-coding ribosomal RNA.