Analysis of Euglena gracilis chloroplast DNA : Mapping of a DNA sequence complementary to 16 S rRNA outside of the three rRNA gene sets

Abstract

It is accepted now that ~~g~e~u gracilis chloroplast DNAcontains 3 rRNA gene sets (I 6 S, 23 S, 5 S RNA) which are located in 3 tandemly repeated DNA segments of 5600 base pairs each [l-3]. Both the repeats and the rRNA genes were mapped on the circular DNA molecule in relation to numerous restriction enzyme cleavage sites and in particular it was shown that the DNA fragments EcoF, EcoL and EcoP (for DNA fragment nomenclature see legend to fig.1 and [3]) hybridized to rRNA. It was also shown that the 16 S rRNA hybridized exclusively to fragment EcoP [2] and that the three sets of genes were arranged from 5’ to 3’ end in the order of 16 S-23 S5 s [4]. However, according to [3,5-81 and contrary to others { 1,2,4] total rRNA hybridized also to the fragment EcoB which according to present mapping data [ 1,2,4] should not carry any structural rRNA genes. We have investigated this problem and give in this report unequivocal experimental evidence that the fragment E’coB does have a short DNA segment complementary to 16 S but not to 23 S rRNA, suggesting that Euglenagracilis chloroplast DNA contains in addition to three complete rRNA gene sets a supplementary 16 S rRNA cistron.