EVOLUTION OF THE ITS SEQUENCES OF RIBOSOMAL DNA IN ENTEROMORPHA (CHLOROPHYCEAE)

Ribosomal DNA (rDNA) region, including the 3' end of the 18S rRNA gene , the entire 5.8S rRNA gene, the 5' end of the 28S rRNA gene, and the internal transcribed spacers ITS 1 and ITS 2, of Enteromorpha green al gae from the Baltic Sea, were sequenced. The evolution of the Enteromo rpha sequences differed from those of other green algae in several imp ortant ways. The ITS regions were short and had a high nucleotide bias . The frequency of nucleotides G and C was up to 70% in the ITS sequen ces, whereas the frequencies were close to 50% in the 5.8S rDNA. Furth ermore, the sequence divergence was much higher in ITS 1 than in ITS 2 . Two haplotypes, differing only by two nucleotides, were detected in the E. intestinalis/compressa complex. The difference coincides with a morphological differentiation (branching of thalli) and may represent distinct gene pools.