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Abstract Detail

Genome Evolution

Georgelis, Nikolaos [1], Braun, Ed L [2], Shaw, Janine R [3], Hannah, L Curtis [3].

The two AGPase subunits evolve at different rates in higher plants, yet they are equally sensitive to activity-altering amino acid changes when expressed in bacteria.

The rate of protein evolution is generally thought to reflect, at least in part, the proportion of amino acids within the protein that are needed for function. In the case of ADP-glucose pyrophosphorylase (AGPase) this premise led to the hypothesis that AGPase small subunit is more conserved compared to the large subunit because a higher proportion of amino acids in the small subunit are required for enzyme activity compared to the large subunit.
Two approaches were taken to test this hypothesis. Using a bacterial expression system, the probability that a random non-synonymous mutation altered AGPase activity was calculated for each subunit of the maize endosperm isoform. Both subunits exhibited the same probability. Second, functional large and small subunit genes from mutagenized libraries were sequenced and the ratio of non-synonymous to synonymous mutations was calculated. This ratio was the same for both subunits. Results indicate that the small and the large subunit AGPase genes are equally predisposed to enzyme activity-altering non-synonymous mutations when expressed in one environment with a single complementary subunit.
As alternative hypotheses, we suggest that the small subunit exhibits more evolutionary constraints in planta than does the large subunit because it is less tissue specific, less redundant and must form functional enzyme complexes with different large subunits. Independent approaches provide data consistent with these alternative hypotheses.

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1 - University of Florida, Plant Molecular and Cellular Biology, 1241 SW 4th AVE #22, Gainesville, FL, 32601, US
2 - University of Florida, Department of Zoology
3 - University of Florida, Plant molecular and Cellular biology

ADP glucose
evolution rate.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P40009
Abstract ID:563

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