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Title: THE REGULATORY FUNCTION OF THE LARGER ISOFORM OF RUBISCO ACTIVASE IS REVEALED BY CARBOXYL TERMINAL DELETION AND A REPLACEMENT OF SINGLE RESIDUE WITH ALANINE

Author
item ZHANG, NING - PLANT BIOLOGY UOI URBANA
item PORTIS JR, ARCHIE

Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/6/1999
Publication Date: N/A
Citation: Zhang, N., Portis Jr, A.R. 1999. The regulatory function of the larger isoform of rubisco activase is revealed by carboxyl terminal deletion and a replacement of single residue with alanine. American Society of Plant Physiologists Meeting: p.165

Interpretive Summary:

Technical Abstract: Rubisco activase is a nuclear encoded chloroplast protein, which is required for the activation of Rubisco in vivo in the presence of its substrate RuBP. In most higher plants examined so far, there are two isoforms of Rubisco activase of unknown functional significance that are formed by alternative splicing during transcription. In Arabidopsis, the longer isoform (46kDa) has 28 additional amino acids at the carboxyl terminus and has little activity at a physiological ADP:ATP ratio of 1:3, whereas the 43kDa isoform retains more than half of its maximal activity. Five deletion mutants of 46kDa isoform were constructed which shortened the protein 7 residues at a time in order to determine if only a part of this domain might be responsible for the difference in nucleotide ration sensitivity. The results revealed that removal of only the last seven residues was sufficient. Residues at position -3~-6 position from the carboxyl terminus were then individually changed to alanine. Analysis of these mutants revealed that only one of the substitutions abolished the greater sensitivity of the 46kDa isoform to ADP. Work is in progress to confirm that the larger isoform regulates the activity of Rubisco activase and thereby the activation state of Rubisco in the manner suggested by these in vitro experiments. Supported by ARS and DOE grant 97ER20268.