A PRELIMINARY COMPARISON OF RESTRICTION FRAGMENT PATTERNS IN THE GENUS CAULERPA (CHLOROPHYTA) AND THE UNIQUE STRUCTURE OF THE CHLOROPLAST GENOME OF CAULERPA SERTULARIOIDES

Comparisons of chloroplast DNA restriction fragments in four species o f Caulerpa revealed that patterns between the species were different, with few and possibly no homologous bands. Two forms of Caulerpa sertu larioides also revealed different patterns, and it is possible that th e forms are separate species. The chloroplast genome in Caulerpa sertu larioides f. sertularioides (S. G. Gmelin) Howe is 131.4 kb in size an d lacks large repeat units. The discovery of another green-algal chlor oplast genome that lacks an inverted repeat indicates that this featur e is either not ancestral to the Chlorophyceae or has been lost severa l times. Several gene clusters commonly found in chloroplast DNAs were found to occur in Caulerpa chloroplast DNA, for example, psbD/C, atpF /H, and psaA/B. The 16S and 23S rRNA, which are typically adjacent, co ntained in an inverted repeat, and cotranscribed, are over 40 kb apart . Genes rps12 and tufA, members of the str operon in eubacteria, are o ver 50 kb in, distance from each other in Caulerpa. The gene order in Caulerpa is unlike any other chloroplast genome characterized to date.