Nucleotide Sequence of Cyanophora paradoxa Cellular and Cyanelle-Associated 5S Ribosomal RNAs

Nucleotide Sequence of Cyanophora paradoxa Cellular and CyanelleAssociated 5s Ribosomal RNAs E. S. MAXWELL," J. LIU,' AND J. M. SHIVELY **' 'Department of Biochemistry North Carolina State University Raleigh, North Carolina 27695 bDepartment of Biological Sciences 336 Long Hall Clemson University Clemson. South Carolina 29631

Cyanophora poradoxa is a flagellated protozoan which has long been of particular interest because of its unique photosynthetic plastid or cyanelle. This cyanelle possesses morphological and genetic characteristics that indicate a close phylogenetic relationship with both prokaryotic cyanobacteria and eukaryotic higher plant chloroplasts!-' It has therefore been postulated that these cyanelles might represent a potential intermediate in photosynthetic plastid evolution between cyanobacteria and plant chloroplasts.' In an effort to understand this evolutionary relationship better, we have isolated and sequenced both the cellular and cyanelle-associated S S ribosomal RNAs. Cyanophoraparudoxa cellular and cyanellar SS rRNAs were 119 and 118 nucleo1). Both exhibited the typical SS rRNA secondary tides in length, respectively (FIGURE structures consisting of five helical regions. Analysis of conserved nucleotides, helix and loop sizes, and defined spacings demonstrated a eukaryotic SS structure for the cellular species and a prokaryotic structure for the cyanellar species.' Sequence comparison of Cyanophoroparodoxacellular and cyanellar SS rRNAs with other 5s rRNA 1. Analysis of the cellular SS rRNA revealed a relatively sequences is shown in TABLE low degree of homology between Cyanophoro and other eukaryotes, indicating a unique position for this organism in evolution. Highest homology was observed with Euglena gracilis SS rRNA. The cyanelle-associated SS rRNA exhibited high homology with both cyanobacterial and chloroplast SS sequences. Highest homology was observed between the cyanellar sequence and the SS rRNAs of the cyanobacterium Synechococcus lividus Interestingly, Synechococcus lividus 111 has been postulated as a possible progenitor of plant chloroplasts because of its unique chloroplastlike SS rRNA secondary structure.6 Sequence results obtained in these experiments are consistent with the idea that the cyanelle could represent an intermediate in chloroplast evolution from endocytosed cyanobacteria as postulated by the endosymbiont hypothesis.' It is impossible to say at this time whether the cyanelle is a direct precursor to chloroplasts (monophyletic event in endocytotic development of the chloroplast) or is the result of a similar but separate endocytotic event (polyphyletic) in photosynthetic plastid development. 'To whom correspondence should be addressed. 559

ANNALS NEW YORK ACADEMY OF SCIENCES

A.

CELLULAR 5 s RNA

B.

CYANELLAR 5s RNA CcAu A C A,

Gc

FIGURE 1. The primary sequence and predicted secondary structure of Cyunophom pumdoxu cellular (A) and cyanellar (B) 5s rRNAs.

561

MAXWELL et al.: NUCLEOTIDE SEQUENCE TABLE 1.

Cyunophoru paradoxu Cellular and Cyanellar 5s rRNA Homologies Cyanophorapamdoxa Cellular 5s rRNA Cyanellar 5s rRNA (% homology) (% homology)

Organism Euglena gracilis Sargassum fulvellum Chlorella pyrenoidosa Acanthamwba castellanii Eisenia bicyclis Tetrahymena thermophilia Spinacia olemcea UIva pertusa Porphyra tenem Gracilaria compress0 Chlamydomonas reinhardtii Synechococcus lividus I1 Synechococcus lividus 111 Marchantia polymorpha chloroplast Pmhlomn Anacystis nidulans Nicotinia tobacum chloroplast Spinacia oleracea chloroplast Lemna minor chloroplast Spirodela oligorhiza chloroplast Bacillus acidocaldarius Rhodospirillum rubrum Chmmatium Euglena gracilis chloroplast Chbmydomonas reinhardtii chloroplast R hodopseudomonasgelatinosa Escherichia coli Chlorobium

79 71 70 70 69 67 65 65 62

60 58

-

-

-

-

-

-

-

78 77 77 74 73 71 71 70 70 67 66 61

60 60 60 59 52

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