Poster: Enzymology

Abs # 256: Sequence and transcript analysis of two distinct Ppc isogenes in the green alga Chlamydomonas reinhardtii

Presenter:	Chollet, Raymond , rchollet1@unl.edu
Authors	Chollet, Raymond  (A)   Mamedov, Tarlan  (A)   Moellering, Eric  (A)
Affiliations:	(A): Dept. of Biochemistry, University of Nebraska-Lincoln

PEP carboxylase (PEPC [Ppc]) is a ubiquitous, cytoplasmic enzyme in green plants and is also widely distributed in bacteria, cyanobacteria, and green algae. PEPC has been purified and characterized in biochemical and immunological terms from two green algae, C. reinhardtii and Selenastrum minutum (see Rivoal et al., JBC, 2001). The data suggest that these microalgae possess at least two distinct classes (1,2) of PEPC that differ significantly from each other and their higher plant and prokaryotic counterparts. However, to date, green-algal PEPC has been essentially unexplored in molecular terms; thus, no information is available on the molecular structure of these novel PEPC isoforms. We found that C. reinhardtii possesses at least two distinct Ppc isogenes, and the corresponding cDNAs were isolated and cloned. Interestingly, the deduced amino-acid sequence of one Ppc cDNA has a green-plant like QNTG motif at its extreme C-terminus, whereas the other has a prokaryotic like motif (RNTG) at the C-terminus. However, the deduced amino-acid sequences of both Ppc cDNAs revealed that the N-terminal phosphorylation domain, typical of green-plant PEPC, is absent. Southern blot and phylogenetic analyses of both C. reinhardtii Ppc isogenes, as well as the effects of different growth conditions (e.g., low/high C_i, low/high inorganic N) on the steady-state transcript levels of these two isogenes and the Class 1 and 2 PEPCs, will be presented.